Ultrasonic biparietal diameter of second trimester Pygmy goat fetuses

Four does pregnant with seven Pygmy goat fetuses were scanned transabdominally from Day 36 to Day 102 of gestation using a real-time ultrasound 5 MHz linear-array scanhead. Fetal biparietal diameter (BPD) was measured on symmetrical frozen images using internal electronic calipers. The relationship between gestational age (GA) in days and BPD in millimeters in Pygmy goat fetuses is expressed as: [GA = 23.2 + 2.08 BPD]. This equation can assign GA to Pygmy goat fetuses of unknown conception dates and allow confinement of does near kidding for induced or observed parturition. Mean kid birthweight was 2.0 + 0.45 kg SEM. These observations are consistent with relationships which have been determined for Toggenburg, Nubian and Angora goat fetuses.     

Real-time ultrasonic biparietal diameter measurement for the prediction of gestational age in llamas

Llama (Lama glama ) fetuses (n = 25) of known gestational age (Day 66 to Day 235) were examined transabdominally using real-time ultrasound with a 5 MHz linear-array scanhead. Maximum head width, or biparietal diameter (BPD), was measured in symmetrical images using electronic linear distance calipers. The fetus was easily located and the BPD measured as early as Day 66 of gestation. During the last trimester, measurement became increasingly difficult due to the posture of the fetus and the limited penetration of the 5 MHz frequency. The relationship between days of gestational age (GA) and mean BPD in millimeters is described by the equation: [GA = 18.8 + 3.79 BPD]. Assignment of gestational age allows estimation of parturition date in this frequently pasture-bred and newly polular domestic ruminant.     

Breed differences in biparietal diameters of second trimester Toggenbubrg, Nubian and Angora goat fetuses

Seven purebred Toggenburg fetuses in four does, six purebred Nubian fetuses in four does, and eight Angora fetuses in six does were repeatedly measured using transabdominal real-time ultrasound with a 5 MH(z) linear-array transducer from 40 d to 100 d gestational age (GA) and their biparietal diameters (BPD) were determined. For Toggenburg goats the GA = 27.9 + 1.64 BPD; for Nubian goats the GA = 26.8 + 1.74 BPD; for Angora goats the GA = 28.6 + 1.77 BPD. The breed differences in GA for equal BPD are insignificant at the beginning of the second trimester but are +3 d for Nubian and +6 d for Angora fetuses by the end of the second trimester.     

Real-time ultrasonic fetal head measurement and gestational age in dairy goats

Dairy breed goat fetuses (n = 219) of known gestational age (Day 39 to Day 100) were examined transabdominally using a real-time ultrasound scanner with a 5 MHz linear-array transducer. Maximum head width was measured in symmetrical images using electronic linear distance calipers. This biparietal diameter (BPD) can be accurately measured as early as Day 40, but measurement becomes difficult after Day 105 of gestation due to the variability of fetal location and posture. The uniform, linear increase in BPD in the second trimester should allow for the accurate assignment of gestational age for doe confinement or induction of kidding.     

Use of fetal biometry to determine fetal age in late pregnancy in llamas

Sixty-three pregnant llamas of known breeding date were used in this study. Forty-six of them were submitted to surgery between 186 and 320 days of gestation (52-91% of average gestation period, respectively). Under general anesthesia their fetuses were exteriorized and fetal weight (W), biparietal diameter (BPD) and femoral (F), tarsus-hoof (T-H), tibial (T)) and fronto-occipital (F-O) length were determined. Additionally, the same variables were determined on 16 newborn llamas. The weight was measured in kg and the length in cm. All the collected data was entered into a spreadsheet and different regression analyses as a function of gestational age (GA) were assessed. The best fit equations and their correlation for linear regression were the following: GA=169.448+16.66(*)W, r=0.99; GA=-51.713+44.77(*)BPD, r=0.88; GA=-72.139+39.48(*)F-O, r=0.71; GA=39.304+8.35(*)T-H, r=0.97; GA=91.276+8.23(*)T, r=0.86; GA=102.029+9.94(*)F, r=0.91. For multiple regression, the dependent variable GA can be predicted by the following equation: GA=67.462+11.163(*)W+20.297(*)BPD. Results of the present study indicated measured variables to be highly correlated with GA. This could be useful on daily basis in clinical examination of the neonates, in assessment of fetal growth and well being with cesarean sections, in the determination of GA in late gestation abortions, and in perinatal and reproductive research in the llama.     

Ultrasound diagnosis of mouse pregnancy and gestational staging

Phenotypic analysis of mutant mice is limited by lack of accurate, simple, and nondestructive in utero imaging techniques. This study evaluated the usefulness of ultrasound imaging (US) to stage fetal mouse gestational age (GA) and depict morphologic development. We imaged 16 pregnant CD-1 mice and a total of 92 fetuses with a 15-MHz US transducer from 9.5 d postcoitus (DPC) until 20.5 DPC or delivery. Parameters recorded included gestational sac dimensions, crown-rump length (CRL), biparietal diameter (BPD), thoracoabdominal diameter (TAD), onset of cardiac activity, and morphologic development. At 9.5 d DPC, all gestations appeared as rounded sacs, with a diameter (mean +/- standard error) of 4.4 +/- 1 mm. BPD, CRL, and GA were highly correlated. The following structures were first identifiable at the following GA: cardiac activity, 10.5 DPC; major cardiovascular structures, 11.5 DPC; limb buds, 10.5 DPC; spine, 12.5 DPC; face and skull ossification, 13.5 DPC; rib ossification, 15.5 DPC; hind- and forelimb digits, 15.5 DPC; stomach and urinary bladder, 17.5 DPC; visualization of the rhombencephalic vesicle, 13.5 DPC; and visualization of the lateral ventricles, 14.5 DPC. The echogenic lungs were distinct from the liver as early as 12.5 DPC. The circle of Willis was detectable with color Doppler as early as 13.5 DPC and was easily visualized at 15.5 DPC. We found that US provides accurate, simple staging criteria for fetal mouse gestational development after 9.5 DPC and may be a nondestructive means of documenting phenotypic alterations in mutant mice in utero.     

Discrepancy in ultrasound biometric parameters of the head (HC--head circumference, BPD--biparietal diameter) in breech presented fetuses

Background: A comparison of fetal ultrasonographic biometric parameters of the head (head circumference - HC, biparietal diameter - BPD) in breech presented fetuses. Methods: Ultrasound biometry was performed in accordance with the method presented in the reference tables. In all breech presented fetuses, the HC, BPD and FL (femur length) were measured. High-risk and multiple pregnancies were excluded from the study. Results: A total of 111 ultrasonographic biometries were performed between the 31(st) - 38(th) week of gestation. Fetuses in the breech position had a significantly lower BPD compared to HC and FL. The difference between BPD and HC was 16.2 days (95%Cl 14.3-18.1; p = 0.001). Maternal age at delivery was 20 - 36 years (average 28.1; median 28.0). Conclusions: According to our results, fetuses in the breech position have a significantly lower BPD compared to HC or FL. HC and FL parameters correlate with gestational age. In cases of ultrasonographic biometric discrepancy between BPD and FL, the fetal position should be taken into account. Breech-presented fetuses have an elongated head shape and ultrasound biometrics should evaluate its circumference (HC). It is important to responsibly interpret the results so as not to stress the expecting mother with suspicions of fetal pathology.     

Ultrasonic measurements of second and third trimester fetuses to predict gestational age and date of parturition in captive and wild spotted hyenas Crocuta crocuta

Parturition in spotted hyenas (Crocuta crocuta) is a fascinating event to witness, as females of this species are highly masculinized and give birth through a penis-like clitoris. Furthermore, shortly after birth, a high rate of aggression occurs between littermates that can sometimes end in siblicide. To study these events thoroughly, an accurate estimate of the date of parturition is necessary. To this end, we performed transabdominal ultrasounds every 20-30 days in five captive spotted hyenas of known gestational age, beginning approximately 30 days after mating. We measured the femur length (FL), abdominal circumference (AC), and biparietal diameter (BPD) of eight fetuses from Days 42 to 100 of their 110 days of gestation. FL proved to be the most effective measurement, as it correlated well with gestational age and was easy to obtain consistently. The relationship between estimated gestational age (EGA) and FL is described by the equation: [EGA = 37.3 + (14.0 x FL)]. AC also correlated well with EGA, but was more difficult to measure than FL. Measuring BPD became increasingly difficult as pregnancies advanced beyond 70 days of gestation. Because gestational age is often not known in captive and free-ranging spotted hyenas, measuring fetal FL ultrasonographically is a rapid and reliable way to determine an approximate date of parturition. This technique proved invaluable when used to track and monitor a free-ranging spotted hyena during the days just before and after parturition.     

Study of prenatal growth in the capuchin monkey (Cebus apella) by ultrasound

Capuchin monkey (Cebus apella) is a new world primate that in recent years has become important in biomedical research. The purpose of this study was to establish and correlate normal fetal growth parameters with gestational age in capuchin monkeys. In seven pregnant animals serial ultrasonic assessment of gestational sac (GS), embryo/fetal greatest length (GL), biparietal diameter (BPD), thorax height (TH), and femur length (FL) were performed. Identification of the GS was possible on day 23+/-2.8 (X +/- SE). The embryo and its heartbeat was detected on day 32.7+/-2.8, the GL being measurable thereafter. By day 45.4+/-1.4 BPD and TH were measurable. FL could only be measured from day 70.6+/-2.1. Predictive regression equations of gestational age (GA) were modeled with data obtained. In addition, preliminary data of fetal heart rate showed a decrease in frequency with advancing gestation.     

Estimation of gestational age in Egyptian native goats by ultrasonographic fetometry

The main aim of the present study was to estimate the gestational age of Egyptian goats by B-mode ultrasound measurement of embryonic or fetal parts throughout pregnancy. Trans-rectal (TR) ultrasonography (7 MHz) was carried out on 15 pregnant Egyptian does at Day 10 post mating on alternate days until Day 25 and then once at 3-5-day intervals until Day 50. Trans-abdominal (TA) ultrasonography (3.5-5 MHz) was carried out on the same animals from Days 25 to 130 at 3-5-day intervals. After imaging the embryo or the fetus, the following parameters were measured: length of the embryo or fetus (CRL), heart rate (FHR), biparital diameter (BPD), trunk diameter (TD), placentome size (PS), umbilical cord diameter (UCD) and femur length (FL). The average of days at which the embryonic vesicle was first determined by TR and TA ultrasonography was 16.98+/-1.97 and 27.87+/-3.48, respectively. The embryo proper with a beating heart was first determined by TR and TA ultrasonography at an average of 22.36+/-2.66 and 30.36+/-4.75 days, respectively. All the fetal measures were significantly (P<0.0001) correlated with the gestational age. With the exception of fetal heart rate (R(2)=0.551), all the measured fetal structures were highly correlated (R(2)> or =90) with the gestational age. In conclusion, the age of embryo or fetus in Egyptian does can be estimated by ultrasound measuring the crown rump length, biparital diameter, trunk diameter, placentome size, umbilical cord diameter and femur length.     

Ingestion of excessive preformed vitamin A by mothers amplifies storage of retinyl esters in early fetal livers of captive Old World monkeys

Excessive preformed vitamin A (VA) intake is contraindicated during pregnancy because of teratogenic concerns. Recent studies have provided biochemical and histologic evidence of chronic hypervitaminosis A in captive Old World monkeys consuming laboratory diets containing high concentrations of retinyl acetate. To investigate the effects of maternal chronic overconsumption of preformed VA on VA storage in early fetal liver, we analyzed monkey fetal livers ranging from 35 to 93 d gestational age (comparable with mid-first to late second trimester in humans) for VA (n = 19) and retinoic acid (n = 9). Retinyl esters were identified in all fetal livers, and retinol, on a percentage basis, was more abundant in younger fetuses. Liver VA concentration increased with gestational age, ranging from 0.0011 to 0.26 micromol/g in the youngest (35 d) and oldest fetuses (93 d), respectively. Liver VA concentrations (mean +/- 1 standard deviation) were 0.023 +/- 0.008 micromol/g in early gestation and 0.19 +/- 0.06 micromol/g in midgestation fetuses. All-trans retinoic acid concentrations were higher in early gestation (99.2 +/- 57.0 pmol/g, n = 6) than in midgestation (18.2 +/- 6.1 pmol/g, n = 3) but were variable. Liver VA concentrations from midgestation fetuses were higher than those in fetal human and monkey livers from later stages of development, when growth and VA accumulation rates are assumed to be highest. Therefore, excessive intake of preformed VA by the mothers results in amplified early fetal liver retinyl ester storage.     

In vitro production of embryos alters levels of insulin-like growth factor-II messenger ribonucleic acid in bovine fetuses 63 days after transfer

The objective of this study was to determine the effect of embryo production systems on the expression of insulin-like growth factor (IGF)-II mRNA in fetal bovine tissues at Day 70 of gestation (63 days after transfer). Oocytes aspirated from ovaries of Holstein cows were matured and fertilized in vitro. Zygotes were cultured in either tissue culture medium (TCM)-199 + 10% estrous cow serum (ECS; in vitro-produced with serum [IVPS]) or TCM-199 + 1% BSA (in vitro-produced with serum restriction [IVPSR]). At 72 h postinsemination, IVPSR embryos were transferred into fresh TCM-199 + 10% ECS whereas IVPS embryos had fresh medium replaced. All embryos were cultured for an additional 96 h. In vivo-produced embryos were harvested from superovulated Holstein cows (multiple ovulations [MO]). Grade 1 blastocysts from all groups were transferred singly into Angus heifers. At Day 70 of gestation, fetuses (n = 14, 13, and 11 for MO, IVPS, and IVPSR, respectively) were collected; liver and skeletal muscle samples were snap frozen, and whole-cell RNA (wcRNA) was extracted. Levels of IGF-II mRNA were determined by RNase protection assay and quantified relative to 18S rRNA (mean arbitrary units +/- SEM). WcRNA from adult and Day 90 fetal bovine liver were used as controls. Adult liver contained 9-fold less IGF-II mRNA than liver from Day 90 fetuses (P < 0.05). Fetal livers of males originating from IVPS and IVPSR groups possessed approximately 2-fold greater levels of mRNA for IGF-II than those from MO males (0.25 +/- 0.07, 0.33 +/- 0.04, and 0.14 +/- 0.03, respectively; P < 0.05). Levels of mRNA for IGF-II tended to be lower (P = 0.07) in skeletal muscle of fetuses originating from the IVPSR group (0.043 +/- 0.005) compared to MO controls (0.070 +/- 0.008). In conclusion, at Day 70 of gestation, fetuses originating from in vitro production systems possessed altered levels of IGF-II mRNA in both liver and skeletal muscle.     

Prediction of gestational age by ultrasonic fetometry in llamas (Lama glama) and alpacas (Lama pacos)

Fetal biparietal diameter (BPD) and thorax height (TH) were measured by ultrasound during intrauterine growth in pregnant llamas (Lama glama) and alpacas (Lama pacos). The goal was to establish representative curves that allows estimation of gestational age (GA) from real-time ultrasonic measurements of these fetal structures at any stage of gestation. Llamas and alpacas were mated under controlled conditions. Ultrasound exams were conducted to determine pregnancy status 1 month later. Measurements of fetal BPD and TH were conducted from the second month of pregnancy until term. Observation and assessment of fetal TH was difficult during the last 3 months of pregnancy, specially in llamas. Regression curves were calculated from the data as a function of GA, with the best fit represented by the following equations: llama GA=(BPD-0.002399)43.02293,r=0.98,P<0.001; llama GA=(TH-0.07137)46.94485, r=0.95,P<0.001; alpaca GA=(BPD-0.11376)47.23287, r=0.98,P<0.001; alpaca GA=(TH-0.36436)52.87663, r=0.96,P<0.001, where GA was measured in days and BPD and TH in centimeters. Results indicate that ultrasonic measurement of these fetal biometric variables constitute a valuable tool to estimate GA at any stage of pregnancy in these domestic South American camelids.     

Impact of periconceptional nutrition on maternal and fetal leptin and fetal adiposity in singleton and twin pregnancies

It has been proposed that maternal nutrient restriction may alter the functional development of the adipocyte and the synthesis and secretion of the adipocyte-derived hormone, leptin, before birth. We have investigated the effects of restricted periconceptional undernutrition and/or restricted gestational nutrition on fetal plasma leptin concentrations and fetal adiposity in late gestation. There was no effect of either restricted periconceptional or gestational nutrition on maternal or fetal plasma leptin concentrations in singleton or twin pregnancies during late gestation. In ewes carrying twins, but not singletons, maternal plasma leptin concentrations in late gestation were directly related to the change in ewe weight that occurred during the 60 days before mating [maternal leptin = 0.9 (change in ewe weight) + 7.8; r = 0.6, P < 0.05]. In twin, but not singleton, pregnancies, there was also a significant relationship between maternal and fetal leptin concentrations (maternal leptin = 0.5 fetal leptin + 4.2, r = 0.63, P < 0.005). The relative mass of perirenal fat was also significantly increased in twin fetal sheep in the control-restricted group (6.0 +/- 0.5) compared with the other nutritional groups (control-control: 4.1 +/- 0.4; restricted-restricted: 4.4 +/- 0.4; restricted-control: 4.3 +/- 0.3). In conclusion, the impact of maternal undernutrition on maternal plasma leptin concentrations during late gestation is dependent on fetal number. Furthermore, we have found that there is an increased fetal adiposity in the twins of ewes that experienced restricted nutrition throughout gestation, and this may be important in the programming of postnatal adiposity.     

The value of urine osmolality as an index of stress in the ovine fetus

In ovine fetuses, during 100-130 days of gestation, urine osmolalities less than 175 mosmol/kg water were associated with plasma immunoreactive adrenocorticotrophin (ACTH) concentrations below 40 pg/ml in 40/41 samples. In 18/29 fetuses with urine osmolalities greater than 175 mosmol/kg water plasma ACTH was significantly elevated. In 38 samples of fetal blood there was a significant correlation between plasma ADH and ACTH concentrations. By least squares regression the equation to the line was [ACTH] = 5.06 + 3.70 [ADH] (r = 0.62, P less than 0.001). In 50 samples from fetuses of gestational ages 100-140 days, with urine osmolalities of 302 +/- 86 mosmol/kg (mean +/- SD) the blood pH, pO2 and pCO2 values were not significantly different from those in 50 samples from fetuses with urine osmolalities of 125 +/- 22 mosmol/kg. It is proposed that the measurement of fetal urine osmolality provides a good index of fetal stress. A fetus with a urine osmolality less than 175 mosmol/kg is almost invariably in the optimum, unstressed condition.     

Determination of gestational age in sheep and goats using transrectal ultrasonographic measurement of placentomes

Three experiments were conducted to determine gestational age in the ewe and doe by measuring placentomes with a B-mode ultrasonograph and a 5 MHz transducer. Transrectal measurements were obtained by placing the female over a bale of hay. In Experiment 1, ewes (n = 12) and does (n = 15) were examined by transrectal ultrasonography every week from breeding to parturition to determine the growth pattern of placentomes during pregnancy. In Experiment 2, placentomes from 132 ewes and 169 does were measured between 30 and 90 d of gestation. A linear regression relationship between fetal age in days and placentome size in mm was calculated and adjusted for does (gestational age = 28.74 + 1.80PL + e, r(2) = 70.34) and for ewes (age = 47.98 + 0.62PL + e, r(2) = 15.59). In Experiment 3, the placentomes of 63 does were measured to validate this relationship by using linear regression. Gestational age was determined correctly in 66% of the does, with a range of +/- 7 d and in 96% with a margin of +/- 14 d. In conclusion, transrectal ultrasonography allowed for the measurement of placentome size, which increased rapidly during the first 70 to 90 d of gestation in ewes and does. In ewes, however, there was a poor correlation of placentome size with gestational age, while in goats, measurement of placentomes could be used along with pregnancy diagnosis by transrectal ultrasonography as an indication of gestation age.     

Use of ultrasound to monitor prenatal growth and development in the common marmoset (Callithrix jacchus)

The increasing use of non-human primates to study fetal development and neonatal management has necessitated the availability of fetuses of known gestational history. In this study, prenatal development and growth were investigated in the common marmoset (Callithrix jacchus) using ultrasound. The objectives of this study were: (1) to determine the accuracy of ultrasound for monitoring prenatal growth and development in common marmosets, (2) to determine if litter size influences prenatal growth trajectories, and (3) to assess growth discordancy among litter mates. Fifty pregnancies were monitored longitudinally using real-time abdominal sonography. During each examination the number of fetuses was recorded, and crown-rump length (CRL) and biparietal diameter (BPD) were measured. The results indicate that ultrasound is a reliable method for observation of gross morphological changes during prenatal development in this species. Measures of CRL and BPD taken early in gestation using ultrasound were in agreement with those from gross specimens. Triplets were significantly (P < 0.05) smaller than twins for both BPD and CRL. No significant relationship was found between litter size and within litter variation in CRL or BPD. This study is the first longitudinal investigation of prenatal growth and development in C. jacchus. The observations from this study will be of use for determining approximate gestational age of fetuses, as well as providing guidelines for routine monitoring of pregnancy in this species. © 1995 Wiley-Liss, Inc.     

Corticotropin releasing hormone concentrations in umbilical cord blood of preterm fetuses.

Corticotrophin releasing hormone (CRH), dehydroepiandrosterone sulfate (DHEAS) and cortisol were measured in umbilical cord plasma obtained from 90 preterm and 98 term fetuses. Maternal plasma was obtained from 23 women who delivered preterm and from 23 women matched for gestational age who ultimately delivered term infants. Mean umbilical cord plasma CRH concentration was significantly higher in the preterm fetuses (n = 69, 538 +/- 63 pg/ml) compared to the term fetuses (n = 98, 280 +/- 22 pg/ml, P < 0.01). Mean DHEAS level in the preterm fetuses was 208 +/- 22 mg/dl (n = 56), cortisol level was 7 +/- 1 mg/dl (n = 58). Umbilical plasma CRH concentrations (808 +/- 170 pg/ml) were significantly higher at 24-27 weeks than at 28-31 or 31-34 weeks gestation. Cortisol levels (12 +/- 3 micrograms/dl) were highest at 24-27 weeks. Mode of delivery and the presence of labor did not affect fetal CRH levels. The highest fetal CRH levels were measured in the pregnancies complicated by hypertension as well as prematurity; however, fetal CRH levels remained higher in the preterm group compared to the term group when hypertensive pregnancies were excluded. Maternal plasma CRH levels were significantly higher in the group that delivered preterm compared to women who delivered at term matched for gestational age (1058 +/- 184 pg/ml compared to 456 +/- 71 pg/ml, P < 0.00).(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of fetal growth by repeated ultrasound measurements in the wild guinea pig (Cavia aperea)

Fetal growth during pregnancy has previously been studied in the domesticated guinea pig (Cavia aperea f. porcellus) after dissecting pregnant females, but there are no studies describing the fetal growth in their wild progenitor, the wild guinea pig (C aperea). In this study, 50 pregnancies of wild guinea pig sows were investigated using modern ultrasound technique. The two most common fetal growth parameters (biparietal diameter [BPD] and crown-rump-length [CRL]) and uterine position were measured. Data revealed similar fetal growth patterns in the wild guinea pig and domesticated guinea pig in the investigated gestation period, although they differ in reproductive milestones such as gestation length (average duration of pregnancy 68 days), average birth weight, and litter mass. In this study, pregnancy lasted on average 60.2 days with a variance of less than a day (0.96 days). The measured fetal growth parameters are strongly correlated with each (R = 0.91; P < 0.001) other and with gestational age (BPD regression equation y = 0.04x − 0.29; P < 0.001 and CRL regression equation y = 0.17x − 2.21; P < 0.01). Furthermore, fetuses in the most frequent uterine positions did not differ in their growth parameters and were not influenced by the mother ID. Our results imply that ultrasound measurement of a single fetal growth parameter is sufficient to reliably estimate gestational age in the wild guinea pig.     

Studies on the endocrinology of parturition: relative steroidogenesis in coexisting genetically dissimilar ovine fetuses, concomitant with the temporal patterns of maternal C18 and C19 steroids and prostaglandin F2 alpha release

Ovine embryos collected from two breeds of ewes possessing different gestational periods [Finnish Landrace (Finn), 145.5 +/- 1.4 days; Rambouillet (Ra), 150.7 +/- 1.3 days] were transferred to common, randomly selected recipients. Fetal plasma samples were collected from mixed-breed (MB, one Finn and one Ra; n = 6) and single-breed (SB, single Finn, n = 3; single Ra, n = 3) chronic fetal preparations during the last trimester. In the MB pregnancy, the Ra sibling had temporal patterns of androstenedione similar to those observed in the Finn co-twin; however, these particular changes were greatly accelerated in comparison to the same day of gestation in SB Ra fetuses. Similarly, temporal patterns of change in unconjugated estrone, estrone sulfate, and 17 beta-estradiol were accelerated by as much as 4.6 to 5 days in Ra fetuses of MB pregnancies when compared to Ra fetuses in the SB pregnancies (P less than 0.001), with no difference noted between Ra and Finn co-twins. Maternal progesterone concentrations changed from 8 to 2 ng/ml, androstenedione from 200 to 400 pg/ml, estrone from 65 to 250 pg/ml, and 15-keto-13,14-dihydroprostaglandin F2 alpha from 200 pg/ml to 6000 pg/ml over the last 4 or 5 days of gestation. Chronic fetal manipulation accelerated parturition, with mean gestational lengths in MB, SB Finn, and SB Ra pregnancies being 141.5 +/- 0.7, 141.7 +/- 0.7, and 149.3 +/- 0.9 days, respectively. In this study fetal endocrine changes were largely controlled in the MB pregnancy by the fetal co-twin exhibiting a shorter gestational period.