Prediction of Maternal Cytomegalovirus Serostatus in Early Pregnancy: A Retrospective Analysis in Western Europe

Background

Cytomegalovirus (CMV) is the most prevalent congenital viral infection and thus places an enormous disease burden on newborn infants. Seroprevalence of maternal antibodies to CMV due to CMV exposure prior to pregnancy is currently the most important protective factor against congenital CMV disease. The aim of this study was to identify potential predictors, and to develop and evaluate a risk-predicting model for the maternal CMV serostatus in early pregnancy.

Methods

Maternal and paternal background information, as well as maternal CMV serostatus in early pregnancy from 882 pregnant women were analyzed. Women were divided into two groups based on their CMV serostatus, and were compared using univariate analysis. To predict serostatus based on epidemiological baseline characteristics, a multiple logistic regression model was calculated using stepwise model selection. Sensitivity and specificity were analyzed using ROC curves. A nomogram based on the model was developed.

Results

646 women were CMV seropositive (73.2%), and 236 were seronegative (26.8%). The groups differed significantly with respect to maternal age (p = 0.006), gravidity (p<0.001), parity (p<0.001), use of assisted reproduction techniques (p = 0.018), maternal and paternal migration background (p<0.001), and maternal and paternal education level (p<0.001). ROC evaluation of the selected prediction model revealed an area under the curve of 0.83 (95%CI: 0.8–0.86), yielding sensitivity and specificity values of 0.69 and 0.86, respectively.

Conclusion

We identified predictors of maternal CMV serostatus in early pregnancy and developed a risk-predicting model based on baseline epidemiological characteristics. Our findings provide easy accessible information that can influence the counseling of pregnant woman in terms of their CMV-associated risk.     

先天性巨细胞病毒感染的研究进展

巨细胞病毒(cytomegalovirus, CMV)在世界范围内均有较高的感染率,是最常见的先天性感染。先天性CMV感染可继发于母体原发性感染或非原发性感染。高达40%～50%的感染新生儿是在妊娠早期原发感染, 之后出现长期后遗症,主要包括先天性CMV感染相关听力损伤和神经后遗症。血清学检查对于确定原发性CMV感染至关重要。产前超声检查发现胎儿异常要警惕先天性CMV感染的可能性,磁共振成像有助于发现CMV相关脑异常。羊膜穿刺术是诊断胎儿CMV感染的金标准。加强育龄妇女及孕妇的卫生健康知识教育、减少CMV感染及抗病毒治疗是目前预防先天性CMV感染的主要措施。更昔洛韦及缬更昔洛韦是目前治疗CMV感染最有效的药物。高免疫球蛋白及CMV疫苗预防先天性 CMV 感染的作用尚无明确结论。     

Human cytomegalovirus infection of placental cytotrophoblasts in vitro and in utero: implications for transmission and pathogenesis

Human cytomegalovirus (CMV) is the leading cause of prenatal viral infection. Affected infants may suffer intrauterine growth retardation and serious neurologic impairment. Analysis of spontaneously aborted conceptuses shows that CMV infects the placenta before the embryo or fetus. In the human hemochorial placenta, maternal blood directly contacts syncytiotrophoblasts that cover chorionic villi and cytotrophoblasts that invade uterine vessels, suggesting possible routes for CMV transmission. To test this hypothesis, we exposed first-trimester chorionic villi and isolated cytotrophoblasts to CMV in vitro. In chorionic villi, syncytiotrophoblasts did not become infected, although clusters of underlying cytotrophoblasts expressed viral proteins. In chorionic villi that were infected with CMV in utero, syncytiotrophoblasts were often spared, whereas cytotrophoblasts and other cells of the villous core expressed viral proteins. Isolated cytotrophoblasts were also permissive for CMV replication in vitro; significantly, infection subsequently impaired the cytotrophoblasts' ability to differentiate and invade. These results suggest two possible routes of CMV transmission to the fetus: (i) across syncytiotrophoblasts with subsequent infection of the underlying cytotrophoblasts and (ii) via invasive cytotrophoblasts within the uterine wall. Furthermore, the observation that CMV infection impairs critical aspects of cytotrophoblast function offers testable hypotheses for explaining the deleterious effects of this virus on pregnancy outcome.     

Cytomegalovirus Seroprevalence in Pregnant Women and Association with Adverse Pregnancy/Neonatal Outcomes in Jiangsu Province,China

Background

In this study, we aimed to determine the provincial population-based seroprevalence in pregnant women and to further explore the association of maternal CMV infection status and adverse pregnancy/neonatal/growth outcomes in Jiangsu, China.

Methods

In this case-control study, the sera from 527 pregnant women with adverse pregnancy/neonatal outcomes and 496 mothers of healthy infants in Jiangsu Province, collected at gestation age of 15–20 weeks, were tested for anti-CMV IgG, IgM and IgG avidity. Adverse pregnancy/neonatal outcomes were identified based on pregnancy/neonatal outcomes.

Results

The overall seroprevalence of anti-CMV IgG was 98.7%, with 99.4% and 98.0% in the case and control groups, respectively (P = 0.039). The prevalence of anti-CMV IgG+/IgM+, was higher in the case group than that in the control group (3.8% vs. 1.6%, P = 0.033). Anti-CMV IgG avidity assay showed that none in the control group were primarily infected, but five (0.9%) in the case group underwent primary infection (P = 0.084); all five infants of these women presented severe adverse neonatal/growth outcomes. Exact logistic regression analysis showed that anti-CMV IgG+/IgM+ was associated with adverse pregnancy/neonatal/growth outcomes (aOR = 2.44, 95% CI 1.01–6.48, P = 0.047). Maternal low education level and prior abnormal pregnancies also were risk factors for adverse pregnancy/neonatal outcomes.

Conclusions

In populations with very high prevalence of latent CMV infection, active maternal CMV infection during pregnancy might be a risk factor for adverse pregnancy/neonatal outcomes.     

Permissive Cytomegalovirus Infection of Primary Villous Term and First Trimester Trophoblasts

Forty percent of women with primary cytomegalovirus (CMV) infections during pregnancy infect their fetuses with complications for the baby varying from mild to severe. How CMV crosses the syncytiotrophoblast, the barrier between maternal blood and fetal tissue in the villous placenta, is unknown. Virus may cross by infection of maternal cells that pass through physical breaches in the syncytiotrophoblast or by direct infection of the syncytiotrophoblast, with subsequent transmission to underlying fetal placental cells. In this study, we show that pure (>99.99%), long-term and healthy (>3 weeks) cultures of syncytiotrophoblasts are permissively infected with CMV. Greater than 99% of infectious progeny virus remained cell associated throughout culture periods up to 3 weeks. Infection of term trophoblasts required a higher virus inoculum, was less efficient, and progressed more slowly than parallel infections of placental and human embryonic lung fibroblasts. Three laboratory strains (AD169, Towne, and Davis) and a clinical isolate from a congenitally infected infant all permissively infected trophoblasts, although infection efficiencies varied. The infection of first trimester syncytiotrophoblasts with strain AD169 occurred at higher frequency and progressed more rapidly than infection of term cells but less efficiently and rapidly than infection of fibroblasts. These results show that villous syncytiotrophoblasts can be permissively infected by CMV but that the infection requires high virus titers and proceeds slowly and that progeny virus remains predominantly cell associated.     

Pregnancy and viral infections: Mechanisms of fetal damage,diagnosis and prevention of neonatal adverse outcomes from cytomegalovirus to SARS-CoV-2 and Zika virus

Some maternal infections, contracted before or during pregnancy, can be transmitted to the fetus, during gestation (congenital infection), during labor and childbirth (perinatal infection) and through breastfeeding (postnatal infection). The agents responsible for these infections can be viruses, bacteria, protozoa, fungi. Among the viruses most frequently responsible for congenital infections are Cytomegalovirus (CMV), Herpes simplex 1–2, Herpes virus 6, Varicella zoster. Moreover Hepatitis B and C virus, HIV, Parvovirus B19 and non-polio Enteroviruses when contracted during pregnancy may involve the fetus or newborn at birth. Recently, new viruses have emerged, SARS-Cov-2 and Zika virus, of which we do not yet fully know the characteristics and pathogenic power when contracted during pregnancy.Viral infections in pregnancy can damage the fetus (spontaneous abortion, fetal death, intrauterine growth retardation) or the newborn (congenital anomalies, organ diseases with sequelae of different severity). Some risk factors specifically influence the incidence of transmission to the fetus: the timing of the infection in pregnancy, the order of the infection, primary or reinfection or chronic, the duration of membrane rupture, type of delivery, socio-economic conditions and breastfeeding. Frequently infected neonates, symptomatic at birth, have worse outcomes than asymptomatic. Many asymptomatic babies develop long term neurosensory outcomes.The way in which the virus interacts with the maternal immune system, the maternal-fetal interface and the placenta explain these results and also the differences that are observed from time to time in the fetal?neonatal outcomes of maternal infections. The maternal immune system undergoes functional adaptation during pregnancy, once thought as physiological immunosuppression. This adaptation, crucial for generating a balance between maternal immunity and fetus, is necessary to promote and support the pregnancy itself and the growth of the fetus. When this adaptation is upset by the viral infection, the balance is broken, and the infection can spread and lead to the adverse outcomes previously described. In this review we will describe the main viral harmful infections in pregnancy and the potential mechanisms of the damages on the fetus and newborn.     

Mother-to-fetus transmission of cytomegalovirus. A review

Congenital human cytomegalovirus (CMV) infection is the leading infectious cause of mental retardation, sensorineural deafness and visual impairment. It is mainly related to a primary maternal infection. The placenta should be considered the most important site of both the protection of the fetus from CMV infection and the transmission of CMV from mother to fetus. The control of the passage of CMV across the placenta probably involves a cascade of regulatory events. Roles are played by factors relating to the host immune-selective pressures, such as local cytokines and maternal CMV-specific neutralizing antibodies. The presence of other pathogens at the maternal-fetal interface also influences the outcome of CMV infection. Further investigations are needed in which clinical CMV strains are applied in in vitro studies to unravel the molecular mechanism of the intrauterine transmission of CMV and to elucidate the complex regulation that leads to prevention of the in utero transmission of CMV in vivo.     

Suppression of cell mediated immunity to cytomegalovirus and tuberculin in pregnancy employing the leukocyte migration inhibition test

To clarify the mechanism of reactivation of cytomegalovirus (CMV) in pregnancy, cell mediated immunity to CMV was investigated in 108 pregnant and 29 postpartal women employing the leukocyte migration inhibition technique. It was demonstrated that CMV-specific cell mediated immunity was suppressed as gestation progressed in 20% of the seropositive women during the first trimester, in 78% during the second trimester and in all at term. The suppression of cell mediated immunity during pregnancy ceased 8 weeks after parturition. The results suggested that reactivation of CMV in pregnancy was probably caused by the suppression of CMV-specific cell mediated immunity.     

Prevalence of maternal cytomegalovirus (CMV) antibody and detection of CMV DNA in amniotic fluid.

The prevalence of cytomegalovirus (CMV) IgG antibody was determined in 573 pregnant women in the first trimester. The overall prevalence of CMV IgG antibody was 77.5%. The rate of seropositivity was 67.7% in women < 25 yr, and increased with age to 85.7% in women 40 yr. These results imply that young women in Japan are at increased risk for primary CMV infection during pregnancy and that congenital CMV infection rates might increase in the future. We conducted a prospective study of 75 pregnant women who underwent amniocentesis for various indications to determine if CMV DNA could be detected in the amniotic fluid. None had symptoms associated with CMV infection, CMV IgM antibody, or seroconversion to CMV IgG antibody during pregnancy. CMV DNA was not detected in the amniotic fluid using a polymerase chain reaction assay. The 65 fetuses, including 3 sets of twins, were followed through birth. CMV DNA was not detected in urine samples obtained within the first 2 weeks of life. In conclusion, CMV DNA was not detected in the amniotic fluid of women who did not have CMV infection. These results, however, suggest that the negative predictive value of prenatal amniotic fluid analysis is high and that the presence of CMV DNA in the amniotic fluid has clinical significance for the diagnosis of congenital CMV infection if detected in pregnant women.     

The placenta as a site of cytomegalovirus infection in guinea pigs.

The development of cytomegalovirus (CMV) infection in the placenta was studied in Hartley guinea pigs inoculated at midgestation, and its role in determining the outcome of fetal CMV infection was assessed. A hematogenous spread of CMV from the mother to the placenta occurred early during the course of the infection. However, the virus remained present in placental tissues long after CMV had been cleared from maternal blood (i.e., 3 and 4 weeks postinoculation). At that time, the virus was able to replicate in placental tissues in the presence of specific maternal antibodies. Viral nucleocapsids were seen within nuclei of trophoblastic cells, and virions were present surrounding infected cells. In addition, typical CMV-induced histopathological lesions bearing CMV antigens were consistently localized at the transitional zone between the capillarized labyrinth and the noncapillarized interlobium. Whenever CMV infection of the fetus occurred, virus was isolated from the associated placenta. Among placental-fetal units with CMV-infected placentas, only 27% of the fetuses were found to be infected. In addition, there was a delay in the establishment of the infection in the fetus in relation to the placenta, although frequencies of virus isolation in placental and fetal tissues peaked at 3 weeks after CMV inoculation. These results suggest that during primary CMV infection of pregnant guinea pigs, the placenta not only serves as a reservoir for CMV but also acts to limit transmission of the virus to the fetus.     

Pathogenesis and vertical transmission of a transplacental rat cytomegalovirus

Background

Cytomegalovirus (CMV) congenital infection is the major viral cause of well-documented birth defects in human. Because CMV is species-specific, the main obstacle to developing animal models for congenital infection is the difference in placental architecture, which preludes virus transmission across the placenta. The rat placenta, resembling histologically to that of human, could therefore facilitate the study of CMV congenital infection in human.

Results

In this report, we present clear evidences of the transplacental property of a new rat CMV (RCMV), namely ALL-03, which had been isolated from placenta and uterus of the house rat. Our study signifies the detection of infectious virus, virus particles, viral protein and DNA as well as immune response to demonstrate a natural model of acute CMV infection including the immunocompetent and immunocompromised host associated with or without pregnancy. It is characterized by a full range of CMV related clinical signs; lesions and anatomical virus distribution to uterus, placenta, embryo, fetus, neonate, lung, kidney, spleen, liver and salivary gland of the infected rats in addition to the virus-specific seroconversion. The preference of the virus for different organs mimics the situation in immunocompromised man. Most interestingly, the placenta was observed to be involved in the maternofetal infection and hence confirmed the hypothesis that the RCMV strain ALL-03 is capable to cross the placenta and infect the offsprings congenitally.

Conclusion

The maternal viremia leading to uterine infection which subsequently infecting to the fetus through the placenta is the most likely phenomenon of CMV vertical transmission in our study.     

Regulation of maternal and fetal hemodynamics by heme oxygenase in mice

Heme oxygenase (HMOX) regulates vascular tone and blood pressure through the production of carbon monoxide (CO), a vasodilator derived from the heme degradation pathway. During pregnancy, the maternal circulation undergoes significant adaptations to accommodate the hemodynamic demands of the developing fetus. Our objective was to investigate the role of HMOX on maternal and fetal hemodynamics during pregnancy in a mouse model. We measured and compared maternal tissue and placental HMOX activity and endogenous CO production, represented by excreted CO and carboxyhemoglobin levels, during pregnancy (Embryonic Days 12.5-15.5) to nonpregnant controls. Micro-ultrasound was used to monitor maternal abdominal aorta diameters as well as blood flow velocities and diameters of fetal umbilical arteries. Tin mesoporphyrin, a potent HMOX inhibitor, was used to inhibit HMOX activity. Changes in maternal vascular tone were monitored by tail cuff blood pressure measurements. Effects of HMOX inhibition on placental structures were assessed by histology. We showed that maternal tissue and placental HMOX activity and CO production were significantly elevated during pregnancy. When HMOX in the placenta was inhibited, maternal and fetal hemodynamics underwent significant changes, with maternal blood pressures increasing. We concluded that increases in maternal tissue and placental HMOX activity contribute to the regulation of peripheral vascular resistance and therefore are important for the maintenance of normal maternal vascular tone and fetal hemodynamic functions during pregnancy.     

Human cytomegalovirus gene products US3 and US6 down-regulate trophoblast class I MHC molecules

The epidemiological correlation between human CMV (HCMV) infection and spontaneous fetal loss has been suggested, but the underlying mechanism is not well understood. Fetal cytotrophoblasts, which are in direct contact with the maternal immune system in the uterus during pregnancy, do not express HLA-A and HLA-B, but express the nonclassical class I HLA-G and HLA-C. It has been shown that both HLA-G and HLA-C are capable of inhibiting NK-mediated cell lysis. In our present study, using human trophoblast cell lines as well as other cell lines stably transfected with the human class I genes, we have demonstrated that HCMV US3 and US6 down-regulate the cell-surface expression of both HLA-G and HLA-C by two different mechanisms. HCMV US3 physically associates with both trophoblast class I MHC species, retaining them in the endoplasmic reticulum. In contrast, HCMV US6 inhibits peptide transport by TAP and thus specifically the intracellular trafficking of class I molecules. Therefore, these findings suggest for the first time a possible molecular mechanism underlying HCMV-related spontaneous pregnancy loss.     

High-risk pregnancy and hypoluteoidism in the bitch

High-risk pregnancies are those in which the prevalence of maternal, fetal and/or perinatal morbidity or mortality is likely to be higher than that of the general obstetrical population. Some maternal characteristics associated with risk to maternal, fetal and/or perinatal health are readily identifiable prior to conception, such as advanced maternal age, brachycephalic breed, or a previous history of pregnancy loss. Others, such as gestational diabetes or a singleton litter, are recognized after conception. Early recognition of the problem (i.e. the risk), anticipation of the potential sequelae, and development of an aggressive management scheme are essential for a successful outcome of a high-risk pregnancy. A previous history of pregnancy loss is a high-risk factor for recurrence during subsequent pregnancies. Infection is a common cause. In some instances, recurrent pregnancy loss is associated with low serum concentrations of progesterone. Although the mechanism(s) by which this occurs is not fully understood, the situation has been called hypoluteoidism. Whatever the cause of the risks to pregnancy, the goals of managing high-risk pregnancies are to optimize maternal, fetal and perinatal health, so as to maintain maternal health throughout pregnancy and lactation and maximize the number of healthy pups surviving to weaning age.     

High-risk pregnancy and hypoluteoidism in the bitch

High-risk pregnancies are those in which the prevalence of maternal, fetal and/or perinatal morbidity or mortality is likely to be higher than that of the general obstetrical population. Some maternal characteristics associated with risk to maternal, fetal and/or perinatal health are readily identifiable prior to conception, such as advanced maternal age, brachycephalic breed, or a previous history of pregnancy loss. Others, such as gestational diabetes or a singleton litter, are recognized after conception. Early recognition of the problem (i.e. the risk), anticipation of the potential sequelae, and development of an aggressive management scheme are essential for a successful outcome of a high-risk pregnancy. A previous history of pregnancy loss is a high-risk factor for recurrence during subsequent pregnancies. Infection is a common cause. In some instances, recurrent pregnancy loss is associated with low serum concentrations of progesterone. Although the mechanism(s) by which this occurs is not fully understood, the situation has been called hypoluteoidism. Whatever the cause of the risks to pregnancy, the goals of managing high-risk pregnancies are to optimize maternal, fetal and perinatal health, so as to maintain maternal health throughout pregnancy and lactation and maximize the number of healthy pups surviving to weaning age.     

Induction of maternal behaviors in primigravid rats by ovariectomy,hysterectomy, or ovariectomy plus hysterectomy: Effect of length of gestation

The effects of terminating pregnancy by means of ovariectomy (O), hysterectomy (H), or ovariectomy plus hysterectomy (OH) at different stages of gestation upon the latency to initiation of maternal behavior were examined in primigravid rats. O, H, or OH on either Day 13 or 17 of pregnancy resulted in an accelerated onset of maternal behaviors (median range = 1.0–2.0 day latency for O, H, or OH animals vs 4.0–5.0 day latency for sham-operated intacts). However, O and H on Day 8 of pregnancy were ineffective in inducing a rapid onset of maternal behavior, while OH on Day 8 of pregnancy only slightly facilitated the onset of maternal behavior when compared to animals sham-operated on Day 8 of pregnancy. O, H, and OH on either Day 13 or 17 of gestation were also significantly more effective in rapidly inducing maternal behaviors than the corresponding surgeries performed on Day 8 of pregnancy. These data suggest that the onset of maternal behavior in the pregnant rat can be rapidly induced after mid-pregnancy by surgical procedures that presumably result in a rapid decline in serum steroids of ovarian origin.     

Seroprevalence of Cytomegalovirus,Epstein Barr Virus and Varicella Zoster Virus among Pregnant Women in Bradford: A Cohort Study

Objective

To estimate the seroprevalence of cytomegalovirus (CMV), Epstein Barr virus (EBV) and varicella zoster virus (VZV) among pregnant women in Bradford by ethnic group and country of birth.

Methods

A stratified random sample of 949 pregnant women enrolled in the Born in Bradford birth cohort was selected to ensure sufficient numbers of White UK born women, Asian UK born women and Asian women born in Asia. Serum samples taken at 24-28 weeks’ gestation were tested for CMV IgG, EBV IgG and VZV IgG. Each woman completed a questionnaire which included socio-demographic information.

Results

CMV seroprevalence was 49% among the White British women, 89% among South Asian UK born women and 98% among South Asian women born in South Asia. These differences remained after adjusting for socio-demographic factors. In contrast, VZV seroprevalence was 95% among women born in the UK but significantly lower at 90% among South Asian women born in Asia. EBV seroprevalence was 94% overall and did not vary by ethnic group/country of birth.

Conclusions

Although about half of White British women are at risk of primary CMV infection in pregnancy and the associated increased risk of congenital infection, most congenital CMV infections are likely to be in children born to South Asian women with non-primary infection during pregnancy. South Asian women born in South Asia are at risk of VZV infection during pregnancy which could produce congenital varicella syndrome or perinatal chickenpox. Differences in CMV and VZV seroprevalence by ethnic group and country of birth must be taken into account when universal immunisation against these viruses is contemplated.     

Evaluation of the indirect and IgM‐capture anti‐human cytomegalovirus IgM ELISA methods as confirmed by cytomegalovirus IgG avidity

Primary cytomegalovirus (CMV) infection during pregnancy often results in congenital CMV infection with severe clinical complications. IgM antibodies are one of the indices of primary infection. The IgG avidity index (AI) is also known to remain low for 3 months after primary infection. Here, we evaluated and compared the performance of CMV IgM and IgG avidity assays. Because sensitivity and specificity reportedly differ between CMV IgM kits, CMV IgM detection was compared between the two commercially available ELISA kits that are most commonly used in Japan. Sera for CMV IgM were first screened using a traditional indirect ELISA kit. Selected samples were then tested for CMV IgM and CMV AI using a CMV IgM‐capture ELISA kit and a CMV IgG avidity assay, respectively. The rate of concordance between the IgM kits was 89% (42/47), indicating the absence of any significant difference. Most of the CMV IgM‐positive plasma samples showed high CMV IgG AI; however, 18 commercially available plasma samples with low CMV IgG AI were all CMV IgM‐positive. One plausible explanation for this discrepancy is that the duration of low IgG AI is shorter than that of IgM positivity. Alternatively, CMV IgM tests may generate pseudo‐positive readouts in cases of congenital infection. Nevertheless, our study confirms that CMV IgG AI can be a reliable indicator of CMV primary infection.     

Role of pregnancy and parturition in induction of maternal behavior in prairie voles (Microtus ochrogaster)

In prairie voles (Microtus ochrogaster), most virgin females are infanticidal. To determine the onset of maternal responsiveness, female prairie voles were tested for maternal behavior as virgins and at different times throughout pregnancy. Female voles that were infanticidal as virgins by and large remained infanticidal throughout pregnancy. In contrast, about 30% of voles that were maternal as virgins became infanticidal during pregnancy. To test whether events associated with parturition facilitate the onset of maternal behavior, females had their litters delivered by Caesarean section within a day of expected delivery or were allowed to give birth naturally with sham surgery occurring shortly before or after birth. Females that gave birth naturally were fully maternal and did not attack unrelated pups, but females subjected to artificial delivery remained infanticidal. This suggests that events closely related to parturition are crucial for full development of maternal behavior in female prairie voles.     

Hormonal basis of hysterectomy-induced maternal behavior during pregnancy in the rat.

Hysterectomy during the last half of pregnancy (i.e., Day 10–19) induces a rapid onset of maternal behavior; ovariectomy in addition to hysterectomy, prevents this effect. Estradiol and progesterone were tested for their ability to restore short-latency maternal behavior in hysterectomized-ovariectomized (HO) females operated on the 10th, 13th, 16th and 19th days of pregnancy. A single injection of either 20 μg/kg or 100 μg/kg estradiol benzoate (EB) immediately following HO either alone or followed by 0.5 mg progesterone (P) 44 hr later restored short-latency maternal behavior similar to that observed following hysterectomy only. The lower dose of EB was found to be equally effective at all stages of pregnancy and P was unnecessary to induce maternal behavior. The effectiveness of EB in inducing maternal behavior was discussed in relation to the hormonal changes which follow hysterectomy during pregnancy and to those which are associated with the normal onset of maternal behavior around parturition.