Experimental fetal anencephaly in the rhesus monkey: effect on gestational length and fetal and maternal plasma steroids

What's Happening When the Pregnancies Are Not Terminated in Case of Anencephalic Fetuses?

Background

To review the obstetric outcomes of pregnancies with anencephalic fetuses when these pregnancies are not terminated and ongoing.

Methods

A retrospective chart review is made of the cases with a prenatal diagnosis of anencephaly and who were opted to continue the pregnancy in 1-year period. The evaluated data included gestational age at diagnosis, gestational age at birth, labor induction rates, cesarean delivery rates, stillbirth, shoulder dystocia rate, antepartum and postpartum hemorrhage.

Results

A total of 28 cases that were selected from 87 cases with the diagnosis of anencephaly are included in the study. The average gestational age at diagnosis was 18 weeks. The average gestational age at birth was 31 weeks (range 23 - 37 weeks). Stillbirths were reported in 32% (9/28). Polyhydramnios developed at six patients and two of them required amniodrainage due to severe polyhydramnios. Vaginal birth was achieved in 67% (19/28) of the patients. Labor induction was applied at total 17 patients and one of them had gone to cesarean section due to failed induction. There were two cases of shoulder dystocia. Nine patients had gone to cesarean delivery. Any other complication was not encountered.

Conclusions

Parents should be counseled in detail about continuation of an anencephalic pregnancy before making their decision. The information about “what an anencephalic pregnancy can lead”' should be given. The redundant cesarean deliveries, polyhydramnios and associated complications, obstetrical hemorrhage risk should be discussed with patients. It should also be emphasized that these maternal risks are for the sake of a non-life expectant baby.

Anencephaly and obstetric outcome beyond the age of viability

Objective To review the obstetric impact and natural history of anencephalic pregnancies beyond the age of viability. Study design A retrospective chart review of all cases with a prenatal diagnosis of anencephaly who delivered after 24 weeks' gestation during the period 1990 until 2016. Obstetric outcomes including mode of delivery, live births, shoulder dystocia, antepartum haemorrhage (APH), postpartum haemorrhage (PPH) and uterine rupture were studied. Results A total of 42 cases were studied. The average gestational age at diagnosis was 22 weeks (range 10-41). The average gestational age at birth was 36 weeks (range 25-44 weeks). Induction of labour was performed in 55% (23/42) of the cases. Livebirths were documented in 40% (17/42) of the cases. The average birth weight was 1597±746 g. The rate of vaginal birth was 69% (29/42), the overall rate of caesarean section was 31% (13/42), with a primary caesarean section in 31% (4/13) and a repeat caesarean section in 69% (9/13) of the patients. There were two cases of shoulder dystocia. No other complications were encountered. Conclusion Overall, anencephaly is not associated with an increased risk of obstetric complications; however, there is a tendency towards delivery via repeated caesarean section in women with a previous uterine scar and anencephaly. The prenatal counselling of potential obstetric outcomes could be of robust value for parents who opt to continue with anencephalic pregnancies.

Endocrine and paracrine regulation of birth at term and preterm

We have examined factors concerned with the maintenance of uterine quiescence during pregnancy and the onset of uterine activity at term in an animal model, the sheep, and in primate species. We suggest that in both species the fetus exerts a critical role in the processes leading to birth, and that activation of the fetal hypothalamic-pituitary-adrenal axis is a central mechanism by which the fetal influence on gestation length is exerted. Increased cortisol output from the fetal adrenal gland is a common characteristic across animal species. In primates, there is, in addition, increased output of estrogen precursor from the adrenal in late gestation. The end result, however, in primates and in sheep is similar: an increase in estrogen production from the placenta and intrauterine tissues. We have revised the pathway by which endocrine events associated with parturition in the sheep come about and suggest that fetal cortisol directly affects placental PGHS expression. In human pregnancy we suggest that cortisol increases PGHS expression, activity, and PG output in human fetal membranes in a similar manner. Simultaneously, cortisol contributes to decreases in PG metabolism and to a feed-forward loop involving elevation of CRH production from intrauterine tissues. In human pregnancy, there is no systemic withdrawal of progesterone in late gestation. We have argued that high circulating progesterone concentrations are required to effect regionalization of uterine activity, with predominantly relaxation in the lower uterine segment, allowing contractions in the fundal region to precipitate delivery. This new information, arising from basic and clinical studies, should further the development of new methods of diagnosing the patient at risk of preterm labor, and the use of scientifically based strategies specifically for the management of this condition, which will improve the health of the newborn.

Developmental and functional biology of the primate fetal adrenal cortex

The unique characteristics of the primate (particularly human) fetal adrenal were first realized in the early 1900s when its morphology was examined in detail and compared with that of other species. The unusual architecture of the human fetal adrenal cortex, with its unique and disproportionately enlarged fetal zone, its compact definitive zone, and its dramatic remodeling soon after birth captured the interest of developmental anatomists. Many detailed anatomical studies describing the morphology of the developing human fetal adrenal were reported between 1920 and 1960, and these morphological descriptions have not changed significantly. More recently, it has become clear that fetal adrenal cortical growth involves cellular hypertrophy, hyperplasia, apoptosis, and migration and is best described by the migration theory, i.e. cells proliferate in the periphery, migrate centripetally, differentiate during their migration to form the functional cortical zones, and then likely undergo apoptosis in the center of the cortex. Consistent with this model, cells of intermediate phenotype, arranged in columnar cords typical of migration, have been identified between the definitive and fetal zones. This cortical area has been referred to as the transitional zone and, based on the expression of steroidogenic enzymes, we consider it to be a functionally distinct cortical zone. Elegant experiments during the 1950s and 1960s demonstrated the central role of the primate fetal adrenal cortex in establishing the estrogenic milieu of pregnancy. Those findings were among the first indications of the function and physiological role of the human fetal adrenal cortex and led Diczfalusy and co-workers to propose the concept of the feto-placental unit, in which DHEA-S produced by the fetal adrenal cortex is used by the placenta for estrogen synthesis. Tissue and cell culture techniques, together with improved steroid assays, revealed that the fetal zone is the primary source of DHEA-S, and that its steroidogenic activity is regulated by ACTH. In recent years, function of the human and rhesus monkey fetal adrenal cortical zones has been reexamined by assessing the localization and ontogeny of steroidogenic enzyme expression. The primate fetal adrenal cortex is composed of three functionally distinct zones: 1) the fetal zone, which throughout gestation does not express 3 beta HSD but does express P450scc and P450c17 required for DHEA-S synthesis; 2) the transitional zone, which early in gestation is functionally identical to the fetal zone but late in gestation (after 25-30 weeks) expresses 3 beta HSD, P450scc, and P450c17, and therefore is the likely site of glucocorticoid synthesis, and 3) the definitive zone, which lacks P450c17 throughout gestation but late in gestation (after 22-24 weeks) expresses 3 beta HSD and P450scc, and therefore is the likely site of mineralocorticoid synthesis. Indirect evidence, based on effects of P450c21 deficiency and maternal estriol concentrations, indicate that the fetal adrenal cortex produces cortisol and DHEA-S early in gestation (6-12 weeks). However, controversy exists as to whether cortisol is produced de novo or derived from the metabolism of progesterone, as data regarding the expression of 3 beta HSD in the fetal adrenal cortex early in gestation are conflicting. During the 1960s, Liggins and colleagues demonstrated that in the sheep, cortisol secreted by the fetal adrenal cortex late in gestation regulates maturation of the fetus and initiates the cascade of events leading to parturition. Those pioneering discoveries provided insight into the mechanism underlying the timing of parturition and therefore were of particular interest to obstetricians and perinatologists confronted with the problems of preterm labor. However, although cortisol emanating from the fetal adrenal cortex promotes fetal maturation in primates as it does in sheep, its role in the regulation of primate parturition, unlike that in sheep

Primate parturition and the role of the maternal circadian system

Several 24-h rhythms have been observed in the mother and in the fetus during primate gestation. In the mother, 24-h rhythms occur in biophysical variables, pregnancy-associated plasma hormones and preparturient myometrial activity. In addition, both pregnant non-human primates and pregnant women deliver preferentially during the night and early morning hours. A crucial question pertaining circadian rhythms is whether 24-h rhythms that may be observed during pregnancy are endogenous in nature and entrained by the light-dark cycle or whether the daily photoperiod is a causal stimulus. Our work has addressed the role of the maternal and fetal circadian system for 24-h rhythms in pregnancy-associated maternal plasma hormones, preparturient myometrial activity and parturition in human and non-human primate pregnancy. In the present review, the results of some of our studies are being discussed in combination with data available from the literature. It is apparent that 24-h rhythms that may be observed during primate pregnancy are determined by the maternal circadian system, suggesting that the developing fetus receives information about the ambient time of the day via the mother. Fetal entrainment by the mother may ensure fetal cooperation so that parturition occurs at the most favorable time of the day. We conclude that the functioning of the maternal circadian system is integral to the pregnant state. Thus, proper care and management of pregnant women and the ultimate outcome of obstetrics may benefit from more timely methodologies. A chronopharmacological attitude towards the prevention of premature labor and the induction and augmentation of labor at term may yield new therapeutic strategies. Such an approach will enable delivery to take place under optimal conditions for mother and child.

In the rhesus monkey placental retention after fetectomy at 121 to 130 days' gestation outlasts the normal duration of pregnancy

OBJECTIVE

Our aim was to reassess the role of the fetus in the initiation of parturition in nonhuman primates. We tested the effect of the removal of the fetus at 121 to 130 days' gestation on the duration of gestation in pregnant rhesus monkeys.

STUDY DESIGN

Nine monkeys underwent fetectomy with the placenta in situ. Five monkeys underwent surgery without removal of the fetus.

RESULTS

In five control monkeys spontaneous vaginal delivery of live fetuses occurred at 163.8 +/- 4.6 days' gestation (mean +/- SD). In four of nine monkeys that underwent fetectomy the placenta delivered spontaneously at 185, 193, 201, and 207 days' gestation. The five remaining monkeys underwent cesarean section at 162, 189, 201, 202, and 219 days' gestation. Duration of placental retention in monkeys that underwent fetectomy (195 +/- 16.1 days' gestation) exceeded that in controls (p less than 0.05). Plasma progesterone and estradiol concentrations were normal for gestational age at fetectomy, indicating continued placental function.

CONCLUSION

We conclude that the presence of a live fetus plays a significant role in the determination of the duration of normal pregnancy in the rhesus monkey.

5-Hydroxyeicosatetraenoic acid, leukotriene C4, and prostaglandin F2 alpha in amniotic fluid before and during term and preterm labor

Arachidonic acid is metabolized by cyclooxygenase leading to prostaglandins and by lipoxygenases leading to hydroxyeicosatetraenoic acids (HETE) and leukotrienes (LT). Prostaglandins are potent uterine constrictors. 5-HETE and LTC4 also stimulate uterine contractions but their role in labor is not known. To estimate the activities of these pathways before parturition and their relationship to uterine contractility, amniotic fluid concentrations of 5-HETE, LTC4, and prostaglandin F2 alpha (PGF2 alpha) were determined in five chronically catheterized rhesus monkeys. Uterine contractility was continually assessed by recording changes in amniotic fluid pressure. The results obtained indicate the following conclusions: (1) 5-HETE and LTC4, but not PGF2 alpha, are associated with uterine contractility after preterm intrauterine surgery. Surprisingly, amniotic fluid PGF2 alpha, levels were nondetectable for 1 to 2 weeks after surgery. (2) 5-HETE and LTC4 are present in higher concentrations than PGF2 alpha in amniotic fluid. (3) 5-HETE, LTC4, and PGF2 alpha all increase with the onset of labor. Amniotic fluid concentrations of 5-HETE and LTC4 are significantly higher than those of PGF2 alpha before and during term and preterm labor. (4) Labor can occur with suppressed PGF2 alpha levels but with increasing 5-HETE and LTC4 levels. (5) These data suggest that 5-HETE and LTC4 are important components of the parturitional process.

Regulation of placental growth and chorionic somatomammotropin in the rhesus monkey: effects of protein deprivation, fetal anencephaly, and placental vessel ligation

An isocaloric protein-deficient diet (0.5 gm/kg of body weight) was administered throughout pregnancy to 10 rhesus monkeys (Macaca mulatta). Ligation of the fetal interplacental bridging vessels (n = 6) and functional fetal hypophysectomy (experimental induction of anencephaly) (n = 10) were performed at midgestation. Monkey chorionic somatomammotropin (mCS) concentrations were measured serially in maternal plasma and in fetal plasma at birth. Fetal weight, trimmed placental weight, and placental DNA content were determined near term in the experimental groups and in controls matched for gestational age. Maternal mCS concentrations rose steadily until term and this rise paralleled the increase in placental weight (mCS at term = 16.5 +/- 0.90 microgram/ml in maternal plasma and 0.024 +/- 0.001 microgram/ml in fetal plasma). At term, maternal mCS correlated with placental DNA (r = 0.61, P less than 0.01) and placental weight (r = 0.49, P less than 0.01), but not fetal weight. Maternal mCS levels were not affected by protein deprivation, fetal anencephaly, or ligation of the interplacental bridging vessels. Maternal protein deprivation had a negative effect on fetal birth weight (409 +/- 22 versus 472 +/- 18 gm for controls, P less than 0.05) and maternal weight gain during pregnancy but had no effect on placental DNA or trimmed placental weight. Fetal anencephaly resulted in a 23% reduction in trimmed placental weight, no change in placental DNA, a 40% reduction in fetal body weight, and a reduced fetal/placental weight ratio. Ligation of interplacental bridging vessels resulted in atrophy of the secondary placental disc, an increase in weight and DNA content of the primary placenta, and normal fetal weight. We have concluded that the hemochorial placenta of the rhesus monkey responds to interruption of the fetal villous circulation in the first half of gestation by initiating compensatory hyperplasia. Placental cellular replication in the second half of rhesus pregnancy in minimally regulated by the fetal central nervous system or the pituitary gland. Secretion of mCS is primarily controlled by the mass of functioning trophoblast.