The intergenerational predisposition to operative delivery

Evolution of the human pelvis and obstructed labor: new explanations of an old obstetrical dilemma

Without cesarean delivery, obstructed labor can result in maternal and fetal injuries or even death given a disproportion in size between the fetus and the maternal birth canal. The precise frequency of obstructed labor is difficult to estimate because of the widespread use of cesarean delivery for indications other than proven cephalopelvic disproportion, but it has been estimated that at least 1 million mothers per year are affected by this disorder worldwide. Why is the fit between the fetus and the maternal pelvis so tight? Why did evolution not lead to a greater safety margin, as in other primates? Here we review current research and suggest new hypotheses on the evolution of human childbirth and pelvic morphology. In 1960, Washburn suggested that this obstetrical dilemma arose because the human pelvis is an evolutionary compromise between two functions, bipedal gait and childbirth. However, recent biomechanical and kinematic studies indicate that pelvic width does not considerably affect the efficiency of bipedal gait and thus is unlikely to have constrained the evolution of a wider birth canal. Instead, bipedalism may have primarily constrained the flexibility of the pubic symphysis during pregnancy, which opens much wider in most mammals with large fetuses than in humans. We argue that the birth canal is mainly constrained by the trade-off between 2 pregnancy-related functions: while a narrow pelvis is disadvantageous for childbirth, it offers better support for the weight exerted by the viscera and the large human fetus during the long gestation period. We discuss the implications of this hypothesis for understanding pelvic floor dysfunction. Furthermore, we propose that selection for a narrow pelvis has also acted in males because of the role of pelvic floor musculature in erectile function. Finally, we review the cliff-edge model of obstetric selection to explain why evolution cannot completely eliminate cephalopelvic disproportion. This model also predicts that the regular application of life-saving cesarean delivery has evolutionarily increased rates of cephalopelvic disproportion already. We address how evolutionary models contribute to understanding and decision making in obstetrics and gynecology as well as in devising health care policies.

Length of labour in mothers and their daughters: A matched cohort study

OBJECTIVE

Physiological length of labour is highly variable and population norms have low sensitivity and specificity for individuals. The birth history of mothers may provide a basis for personalized assessment of labour progress in their nulliparous daughters. This study was designed to investigate the relationship between length of labour in nulliparous daughters and in their mother's first birth, as a basis for constructing individualised labour prediction models in future.

STUDY DESIGN

A mother-daughter matched cohort study was conducted in two Israeli maternity hospitals. Recruitment took place between September 2014 and June 2015 via antenatal clinics. Inclusion criteria were nulliparous daughters with singleton pregnancies at ≥32 weeks' gestation and mothers of included daughters who had a first birth in hospital prior to 1997. Data were collected prospectively for daughters by questionnaire and from electronic hospital records, and through retrospective recall questionnaires for mothers. Mother-daughter length of labour data were analysed using parametric and non-parametric tests and logistic regression. Length of labour was categorized as ≤10 h and >10 h. Other factors influencing daughters' length of labour were also examined.

RESULTS

Data from 323 mother-daughter pairs were analysed. Univariate logistic regression analysis showed that daughters of mothers who were in active labour for more than 10 h showed increased likelihood of having a longer labour [OR1.91 (95 % CI 1.19, 3.05, P = 0.007)]. Controlling for infant gender increased the effect size [OR3.23 (95 % CI 1.55, 6.74, P = 0.002)]. Multivariable logistic regression indicated that mothers' length of labour [OR1.88 (95 % CI 1.12, 3.17)] and daughters' age [OR1.08 (95 % CI 1.02, 1.14)], weight gain in pregnancy [OR1.10 (95 % CI 1.04, 1.16)] and use of anesthesia, were statistically significant factors for daughters' length of labour, with sensitivity, specificity, and positive and negative predictive values of 74 %, 56 %, 66 %, and 64 %, respectively.

CONCLUSIONS

A strong positive association between mother and daughter lengths of labour was found. A model that includes length of labour in their mother's first birth might be useful for labour progress prediction for nulliparous women. Practitioners could inquire about maternal first birth patterns as an additional heuristic to guide practice and increase precision in the clinical management of nullipara women's labour and delivery.

Cliff-edge model predicts intergenerational predisposition to dystocia and Caesarean delivery

The cliff-edge model explains the evolutionary persistence of relatively high incidences of fetopelvic disproportion (FPD), the mismatch of fetal and maternal dimensions during human childbirth. It also predicts that FPD rates have increased evolutionarily since the regular use of Caesarean sections. Here we show that the model also explains why women born by Caesarean because of FPD are about twice as likely to develop FPD in their own childbirth compared with women born vaginally. This theoretical prediction of a complex epidemiological pattern lends support to the cliff-edge model and its underlying assumptions.

Recently, we presented the cliff-edge model to explain the evolutionary persistence of relatively high incidences of fetopelvic disproportion (FPD) in human childbirth. According to this model, the regular application of Caesarean sections since the mid-20th century has triggered an evolutionary increase of fetal size relative to the dimensions of the maternal birth canal, which, in turn, has inflated incidences of FPD. While this prediction is difficult to test in epidemiological data on Caesarean sections, the model also implies that women born by Caesarean because of FPD are more likely to develop FPD in their own childbirth compared with women born vaginally. Multigenerational epidemiological studies indeed evidence such an intergenerational predisposition to surgical delivery. When confined to anatomical indications, these studies report risks for Caesarean up to twice as high for women born by Caesarean compared with women born vaginally. These findings provide independent support for our model, which we show here predicts that the risk of FPD for mothers born by Caesarean because of FPD is 2.8 times the risk for mothers born vaginally. The congruence between these data and our prediction lends support to the cliff-edge model of obstetric selection and its underlying assumptions, despite the genetic and anatomical idealizations involved.

The childhood obesity epidemic as a result of nongenetic evolution: the maternal resources hypothesis

Over the past century, socioenvironmental evolution (eg, reduced pathogenic load, decreased physical activity, and improved nutrition) led to cumulative increments in maternal energy resources (ie, body mass and adiposity) and decrements in energy expenditure and metabolic control. These decrements reduced the competition between maternal and fetal energy demands and increased the availability of energy substrates to the intrauterine milieu. This perturbation of mother-conceptus energy partitioning stimulated fetal pancreatic β-cell and adipocyte hyperplasia, thereby inducing an enduring competitive dominance of adipocytes over other tissues in the acquisition and sequestering of nutrient energy via intensified insulin secretion and hyperplastic adiposity. At menarche, the competitive dominance of adipocytes was further amplified via hormone-induced adipocyte hyperplasia and weight-induced decrements in physical activity. These metabolic and behavioral effects were propagated progressively when obese, inactive, metabolically compromised women produced progressively larger, more inactive, metabolically compromised children. Consequently, the evolution of human energy metabolism was markedly altered. This phenotypic evolution was exacerbated by increments in the use of cesarean sections, which allowed both the larger fetuses and the metabolically compromised mothers who produced them to survive and reproduce. Thus, natural selection was iatrogenically rendered artificial selection, and the frequency of obese, inactive, metabolically compromised phenotypes increased in the global population. By the late 20th century, a metabolic tipping point was reached at which the postprandial insulin response was so intense, the relative number of adipocytes so large, and inactivity so pervasive that the competitive dominance of adipocytes in the sequestering of nutrient energy was inevitable and obesity was unavoidable.

The obstetric dilemma: an ancient game of Russian roulette, or a variable dilemma sensitive to ecology?

The difficult birth process of humans, often described as the "obstetric dilemma," is commonly assumed to reflect antagonistic selective pressures favoring neonatal encephalization and maternal bipedal locomotion. However, cephalo-pelvic disproportion is not exclusive to humans, and is present in some primate species of smaller body size. The fossil record indicates mosaic evolution of the obstetric dilemma, involving a number of different evolutionary processes, and it appears to have shifted in magnitude between Australopithecus, Pleistocene Homo, and recent human populations. Most attention to date has focused on its generic nature, rather than on its variability between populations. We re-evaluate the nature of the human obstetric dilemma using updated hominin and primate literature, and then consider the contribution of phenotypic plasticity to variability in its magnitude. Both maternal pelvic dimensions and fetal growth patterns are sensitive to ecological factors such as diet and the thermal environment. Neonatal head girth has low plasticity, whereas neonatal mass and maternal stature have higher plasticity. Secular trends in body size may therefore exacerbate or decrease the obstetric dilemma. The emergence of agriculture may have exacerbated the dilemma, by decreasing maternal stature and increasing neonatal growth and adiposity due to dietary shifts. Paleodemographic comparisons between foragers and agriculturalists suggest that foragers have considerably lower rates of perinatal mortality. In contemporary populations, maternal stature remains strongly associated with perinatal mortality in many populations. Long-term improvements in nutrition across future generations may relieve the dilemma, but in the meantime, variability in its magnitude is likely to persist.

Oxytocin and catechol-O-methyltransferase receptor genotype predict the length of the first stage of labor

OBJECTIVE

We aimed to identify genetic factors that influence the rate of the first stage of labor.

STUDY DESIGN

We prospectively enrolled 233 laboring nulliparous parturients. Demographic, clinical, and genetic data were collected. We evaluated the influence of population and individual variability using a nonlinear mixed effects model.

RESULTS

Parturients who were homozygous for "G" at oxytocin receptor gene rs53576 transitioned to active labor later and thus had slower labor. Catechol-O-methyltransferase rs4633 genotype TT was associated with slower latent phase labor. Labor induction with prostaglandin was associated with faster labor, and request for meperidine was associated with slower labor. Birthweight was related inversely to the rate of the active phase.

CONCLUSION

There are demographic, clinical, and genetic factors that influence an individual's rate of labor progress. This information could be used in automated form to improve the prediction of the length of the first stage of labor.

A Review of Factors Associated With Dystocia and Cesarean Section in Nulliparous Women

The primary indication for cesarean section in nulliparous women continues to be clinical diagnoses that fall under the rubric of dystocia. These diagnoses account for approximately two-thirds of all cesareans experienced by otherwise healthy nulliparous women. Contemporary research evidence suggests that this clinical phenomenon is complex and multifactorial. This review explores factors associated with the phenomenon of dystocia in the context of a conceptual model that considers women's physical and psychological characteristics, fetal factors, intrapartum care and interventions, assessments and clinical decision-making of health care providers, the sociopolitical environment, and the social and physical environment of childbirth. Clinical recommendations include emphasis on the maintenance of normal weight and weight gain during pregnancy, delaying the admission of nulliparous women to the hospital until active labor is established, avoiding elective induction for nulliparous women, keeping women well-hydrated and well-fed during labor, providing high-quality supportive care during labor, staying the course with effective treatment when dystocia is encountered, and a renewed emphasis on the psychobehavioral preparation of nulliparous women for the realities of labor.

Genetic evidence of multiple loci in dystocia--difficult labour

BACKGROUND

Dystocia, difficult labour, is a common but also complex problem during childbirth. It can be attributed to either weak contractions of the uterus, a large infant, reduced capacity of the pelvis or combinations of these. Previous studies have indicated that there is a genetic component in the susceptibility of experiencing dystocia. The purpose of this study was to identify susceptibility genes in dystocia.

METHODS

A total of 104 women in 47 families were included where at least two sisters had undergone caesarean section at a gestational length of 286 days or more at their first delivery. Study of medical records and a telephone interview was performed to identify subjects with dystocia. Whole-genome scanning using Affymetrix genotyping-arrays and non-parametric linkage (NPL) analysis was made in 39 women exhibiting the phenotype of dystocia from 19 families. In 68 women re-sequencing was performed of candidate genes showing suggestive linkage: oxytocin (OXT) on chromosome 20 and oxytocin-receptor (OXTR) on chromosome 3.

RESULTS

We found a trend towards linkage with suggestive NPL-score (3.15) on chromosome 12p12. Suggestive linkage peaks were observed on chromosomes 3, 4, 6, 10, 20. Re-sequencing of OXT and OXTR did not reveal any causal variants.

CONCLUSIONS

Dystocia is likely to have a genetic component with variations in multiple genes affecting the patient outcome. We found 6 loci that could be re-evaluated in larger patient cohorts.

Progesterone receptor genotype, family history, and spontaneous preterm birth

OBJECTIVE

To examine whether women with a personal or family history of preterm birth are more likely to have genetic variation in the human progesterone receptor (hPR).

METHODS

Women with a singleton preterm birth at less than 37 weeks of gestation between 2002 and 2006 were identified from a prospectively collected clinical and biologic obstetric database (cases). Women in the control group were those with only term deliveries at or above 38 weeks of gestation. The Utah Population Database was queried for family history (first- or second-degree relative) of preterm birth. DNA was extracted from stored buffy coats and genotyped for six single nucleotide polymorphisms in the hPR.

RESULTS

One hundred fifty-four patients (92 women in the preterm case group, 62 women in the term control group) were included. All were white or Hispanic. There were no statistical differences between white and Hispanic allele frequencies. Women in the preterm case group were more likely to carry the minor allele, G (minor allele frequency 0.29 compared with 0.18, P=.035) for rs471767, and were more likely to carry the GT haplotype across rs471767 and rs578029 compared with women in the term control group. Similar haplotype block variation was seen among women with preterm birth plus a family history of preterm birth.

CONCLUSION

Allele and haplotype frequencies in the hPR are significantly different among women with preterm birth and women with preterm birth plus a family history of preterm birth. This suggests the hPR gene may be a candidate for association with preterm birth or familial preterm birth.

LEVEL OF EVIDENCE

III.

Interaction of human Thy-1 (CD 90) with the integrin αvβ3 (CD51/CD61): an important mechanism mediating melanoma cell adhesion to activated endothelium

The expression of the alphavbeta3 integrin (CD51/CD61) on human melanoma cells has been shown to be associated most closely with tumor progression and metastases formation in melanoma. Here, we demonstrated a specific interaction of the alphavbeta3 integrin on melanoma cells with the human Thy-1, an inducible cell adhesion molecule expressed on the cell surface of activated endothelial cells (EC). The interaction was shown by the binding of purified Thy-1 protein to alpha(V)beta(3) transfected cells, to alphavbeta3-expressing melanoma cells and to purified alpha(V)beta(3) integrin. Moreover, melanoma cells adhere specifically to Thy-1 transfectants via alphavbeta3 on melanoma cells showing the functional relevance of this interaction for cell adhesion. Finally, the importance of the alphavbeta3/Thy-1 interaction for the adhesion of melanoma cells to the activated endothelium was confirmed under static and flow conditions by the inhibition of melanoma cell adhesion to and transmigration across activated EC by blocking the alphavbeta3/Thy-1 interaction. In conclusion, we have identified a new pair of adhesion molecules Thy-1 and alphavbeta3 mediating the interaction of melanoma cells and activated EC. These data explain at least in part the high tumorigenicity of alphavbeta3-expressing melanoma cells and the association of alphavbeta3-positive melanoma cells with a high risk of metastasis and poor prognosis.

Genetic influence on dystocia

BACKGROUND

Dystocia-prolonged and difficult labor-is a common and worldwide problem during parturition. Epidemiological studies have suggested a familial aggregation. This study aimed to quantify the genetic influence (i.e. the heritability) on dystocia.

METHODS

A retrospective study of all births in Sweden from 1973 through 1997 was undertaken. Data from the population-based Swedish Birth, Twin and National Family Registers were linked on an individual basis. In total, 2,539,534 births were analyzed. Relationships between sibling and mother-daughter pairs were established. The relative risk for dystocia was calculated. Model-fitting (Mx) was used to estimate the relative contribution of genetic and environmental factors for liability to dystocia.

RESULTS

In all, 190,747 women were diagnosed with dystocia. Measures of familial similarity (relative risks and correlation of liability) for dystocia were higher in monozygotic than in dizygotic twins, other sibling pairs and mother-daughter pairs. Correlation of liability was also higher in full-sisters than in half-sisters. Model-fitting suggested that genetic effects accounted for 28%[95% confidence interval (CI) 21-32] of the susceptibility for dystocia.

CONCLUSION

Dystocia is a complex disorder of poor uterine action that is influenced by a significant genetic component as well as environmental factors. The amount of genetic influence makes it interesting to study the gene expression in these patients. Detection of the genes related to dystocia might lead to better pathophysiological understanding of this condition and the possibility of detecting these mothers before parturition.

Paternal and maternal components of the predisposition to preeclampsia

BACKGROUND

There is an inherited maternal predisposition to preeclampsia. Whether there is a paternal component, however, is not known.

METHODS

We used records of the Utah Population Database to identify 298 men and 237 women born in Utah between 1947 and 1957 whose mothers had had preeclampsia during their pregnancy. For each man and woman in the study group, we identified two matched, unrelated control subjects who were not the products of pregnancies complicated by preeclampsia. We then identified 947 children of the 298 male study subjects and 830 children of the 237 female study subjects who had been born between 1970 and 1992. These children were matched to offspring of the control subjects (1950 offspring of the male control group and 1658 offspring of the female control group). Factors associated with preeclampsia were identified, and odds ratios were calculated with the use of stepwise logistic-regression analysis.

RESULTS

In the group whose mothers had had preeclampsia (the male study group), 2.7 percent of the offspring (26 of 947) were born of pregnancies complicated by preeclampsia, as compared with 1.3 percent of the offspring (26 of 1973) in the male control group. In the female study group, 4.7 percent of the pregnancies (39 of 830) were complicated by preeclampsia, as compared with 1.9 percent (32 of 1658) in the female control group. After adjustment for the offspring's year of birth, maternal parity, and the offspring's gestational age at delivery, the odds ratio for an adult whose mother had had preeclampsia having a child who was the product of a pregnancy complicated by preeclampsia was 2.1 (95 percent confidence interval, 1.0 to 4.3; P=0.04) in the male study group and 3.3 (95 percent confidence interval, 1.5 to 7.5; P=0.004) in the female study group.

CONCLUSIONS

Both men and women who were the product of a pregnancy complicated by preeclampsia were significantly more likely than control men and women to have a child who was the product of a pregnancy complicated by preeclampsia.

Maternal birth weight and cesarean delivery in four race-ethnic groups

OBJECTIVE

We hypothesized that maternal birth weight was associated with the risk of cesarean delivery for nulliparous women.

STUDY DESIGN

In a population-based cohort study, maternal birth data were linked to a Washington State database, including the birth certificates of 18,905 first-born singleton infants (1987-1995).

RESULTS

Among non-Hispanic white subjects, maternal birth weight of 2500 to 3999 g was associated with a 20.9% risk of cesarean delivery, which was the lowest risk, compared with 24.5% for a maternal birth weight <2500 g (P <.05) and 24.0% for a maternal birth weight > or =4000 g (P <.05). Similar patterns of risk were noted among Hispanic and Native American subjects, although the associations did not reach statistical significance. Risk of cesarean delivery was not associated with maternal birth weight among African American subjects. Among non-Hispanic white subjects, the risk of cesarean delivery was 3.23 times greater with a maternal birth weight <2500 g and an infant birth weight > or =4000 g compared with pregnancies with both maternal and infant birth weights between 2500 and 3999 g (P <. 001). Adjustment for socioeconomic factors did not alter these results.

CONCLUSION

Low and high maternal birth weights exert an intergenerational risk of cesarean delivery in nulliparous non-Hispanic white women.

No mutations found in candidate genes for dystocia

Dystocia is a disorder characterized by prolonged or dysfunctional labour. Delivery that starts late or not at all, leads to an increased risk for Caesarean section, infant morbidity and mortality. Familial aggregations of dystocia suggest a polygenic background. We have studied three candidate genes for dystocia, i.e. the genes for testosterone 5-alpha reductase type 1, prostaglandin F2alpha receptor and endothelin 1 and performed mutational screening in 23 women with dystocia, of which 12 have affected relatives. No mutations were found, making it unlikely that any of these genes represent a major cause of dystocia in man.