The role of the placenta in spontaneous preterm labor and delivery with intact membranes

OBJECTIVES

To determine whether placental vascular pathology and impaired placental exchange due to maturational defects are involved in the etiology of spontaneous preterm labor and delivery in cases without histologic acute chorioamnionitis.

METHODS

This was a retrospective, observational study. Cases included pregnancies that resulted in spontaneous preterm labor and delivery (<37 weeks), whereas uncomplicated pregnancies that delivered fetuses at term (≥37-42 weeks of gestation) were selected as controls. Placental histological diagnoses were classified into three groups: lesions of maternal vascular malperfusion, lesions of fetal vascular malperfusion, and placental microvasculopathy, and the frequency of each type of lesion in cases and controls was compared. Moreover, we specifically searched for villous maturational abnormalities in cases and controls. Doppler velocimetry of the umbilical and uterine arteries were performed in a subset of patients.

RESULTS

There were 184 cases and 2471 controls, of which 95 and 1178 had Doppler studies, respectively. The frequency of lesions of maternal vascular malperfusion was greater in the placentas of patients with preterm labor than in the control group [14.1% (26/184) vs. 8.8% (217/2471) (p=0.023)]. Disorders of villous maturation were more frequent in the group with preterm labor than in the control group: 41.1% (39/95) [delayed villous maturation in 31.6% (30/95) vs. 2.5% (13/519) in controls and accelerated villous maturation in 9.5% (9/95) vs. none in controls].

CONCLUSIONS

Maturational defects of placental villi were associated with approximately 41% of cases of unexplained spontaneous preterm labor and delivery without acute inflammatory lesions of the placenta and with delivery of appropriate-for-gestational-age fetuses.

Maternal stress, low cervicovaginal β-defensin, and spontaneous preterm birth

Background

Spontaneous preterm birth (sPTB) is a major contributor to infant mortality and its etiology remains poorly understood. Host immunity and maternal stress may play a role in the pathogenesis of sPTB but mechanisms are poorly delineated. Antimicrobial proteins in the cervicovaginal space, such as beta defensins, modulate immune responses to bacteria and have been shown to modulate the risk of sPTB from non-optimal microbiota. While stress is known to induce immunological changes, no study has examined the interplay between maternal stress and the immune response in association with sPTB.

Objectives

Our objectives were to determine whether psychosocial stress was associated with a mediator of the immune system in the cervicovaginal space, beta defensin-2, and to examine the combined impact of high stress and low cervicovaginal beta defensin-2 levels on the odds of sPTB.

Study Design

From the Motherhood & Microbiome cohort study (n=2000), we performed a secondary, nested case-control study, frequency matched by race/ethnicity, of 519 pregnant women (110 sPTB and 409 term). Stress and cervicovaginal beta defensin-2 levels were measured at 16-20 weeks of gestation. Stress was dichotomized at a score of 30 on Cohen's Perceived Stress Scale (PSS-14). We measured cervicovaginal beta defensin-2 levels with ELISA and dichotomized at the median. We modeled associations of high stress and low cervicovaginal beta defensin-2 levels using multivariable logistic regression. We also compared the proportion of women with high stress and low cervicovaginal beta defensin-2 levels among women with spontaneous preterm and term births using Chi-Square tests. We modeled adjusted associations of stress and cervicovaginal beta defensin-2 levels with odds of sPTB using logistic regression.

Results

The majority of the study population was non-Hispanic black (72.8%), insured by Medicaid (51.1%), and had a PSS-14 score < 30 (80.2%). High stress was associated with reduced adjusted odds of low beta defensin-2 levels (aOR 0.63, 95% CI: 0.38 -0.99). In a model adjusted for race and smoking, both high stress (aOR 1.72, 95% CI: 1.03-2.90) and low beta defensin-2 (aOR 1.58, 95% CI: 1.004-2.49) were associated with increased odds of sPTB. We then built a model of the four possible combinations of low and high stress and low and high beta defensin-2 levels with the odds of sPTB. Women with either high stress (aOR 1.37, 95% CI: 0.68 - 2.78) or low beta defensin-2 (aOR 1.40, 95% CI: 0.83-2.34), had slightly elevated but not significantly increased odds of sPTB compared to women with neither exposure. However, women with both high stress and low beta defensin-2 had significantly elevated odds of sPTB compared to women with neither exposure (aOR 3.16, 95 % CI: 1.46 - 6.84).

Conclusion

High perceived stress and low cervicovaginal beta defensin-2 levels are associated with higher odds of sPTB, and when present concurrently, they result in the highest odds of sPTB in a largely non-Hispanic black cohort. Our findings warrant further work to examine social determinants of health and the host cervicovaginal immune responses that may modulate the pathogenesis of sPTB.