Neonatal morbidity and mortality in birth centers in the United States 2018-2021: An observational study of low-risk birthing individuals.

BACKGROUND: Many studies reporting neonatal outcomes in birth centers include births with risk factors not acceptable for birth center care using the evidence-based CABC criteria. Accurate comparisons of outcomes by birth setting for low-risk patients are needed. METHODS: Data from the public Natality Detailed File from 2018 to 2021 were used. Logistic regression, including adjusted and unadjusted odds ratios, compared neonatal outcomes (chorioamnionitis, Apgar scores, resuscitation, intensive care, seizures, and death) between centers and hospitals. Covariates included maternal diabetes, body mass index, age, parity, and demographic characteristics. RESULTS: The sample included 8,738,711 births (8,698,432 (99.53%) in hospitals and 40,279 (0.46%) in birth centers). There were no significant differences in neonatal deaths (aOR 1.037; 95% CI [0.515, 2.088]; p-value 0.918) or seizures (aOR 0.666; 95% CI [0.315, 1.411]; p-value 0.289). Measures of morbidity either not significantly different or less likely to occur in birth centers compared to hospitals included chorioamnionitis (aOR 0.032; 95% CI [0.020, 0.052]; p-value < 0.001), Apgar score < 4 (aOR 0.814, 95% CI [0.638, 1.039], p-value 0.099), Apgar score < 7 (aOR 1.075, 95% CI [0.979, 1.180], p-value 0.130), ventilation >6 h (aOR 0.349; [0.281,0.433], p-value < 0.001), and intensive care admission (aOR 0.356; 95% CI [0.328, 0.386], p-value < 0.001). Birth centers had higher odds of assisted neonatal ventilation for <6 h as compared to hospitals (aOR 1.373; 95% CI [1.293, 1.457], p-value < 0.001). CONCLUSION: Neonatal deaths and seizures were not significantly different between freestanding birth centers and hospitals. Chorioamnionitis, Apgar scores < 4, and intensive care admission were less likely to occur in birth centers.

Microstructure and mechanics of the chorioamnion membrane with an emphasis on fracture properties.

The normal mechanical functioning of an intact chorioamnion (CA) membrane is essential to successful human reproduction. The amnion and the chorion, separately and together as the bilayer chorioamnion, serve barrier and container functions throughout gestation, and these two important roles are required from conception to birth. The event associated with the "breaking of waters" is a landmark event in labor and delivery. Mechanical rupture of the CA membrane is part of the natural sequence of term delivery, but has serious implications when rupture occurs prior to term; preterm premature rupture of the CA membrane (PPROM) is associated with one-third of premature births. The current manuscript reviews PPROM from a clinical, anatomical, and mechanical perspective with a special focus on the clinically relevant fracture properties of these membranes. Emphasis is given to the link between membrane structure and properties at macroscopic and microscopic length scales. Because it has been demonstrated that the mechanical properties of prematurely failed membranes are not different from membranes of the same gestational age that have remained intact, membrane failure is a local process that must be explored in terms of local changes in structure and properties of isolated portions of the membrane. Future diagnostic techniques aimed at detection of changes in membrane structure (including thickness) and altered mechanical stiffness or strength may allow for prefailure diagnosis of membrane weak spots, thus opening the door for potential intervention and treatment techniques for preterm membrane rupture.

Premature rupture of the fetal membranes: is the amnion the major determinant?

OBJECTIVE: The objective of the study was to evaluate the relative contributions of amnion and chorion to the strength of fetal membranes and to correlate these findings with gestational age. STUDY DESIGN: Fetal membranes from 78 pregnancies were tested for biaxial puncture force using a blunt, instrumented probe with a low-force load cell connected through a load cell conditioner to an oscilloscope. The average of 2 to 4 tests performed on independent regions of the membrane was recorded. Means and SDs were calculated through the gestational age ranges of less than 32, 32 to 36, or 37 weeks or longer. Linear regression analysis was performed across gestational age after grouping data by labor and mode of delivery. RESULTS: There were trends toward decreasing puncture force with gestational age for both chorioamnion and amnion for both vaginal deliveries and cesarean sections. The trends were significant by linear regression for labored deliveries but not unlabored cesarean sections for both chorioamnion and amnion alone. There was no trend in chorion puncture force with either gestational age or delivery mode and the mean puncture force values were, on average, half those for the amnion. CONCLUSION: The amnion is significantly stronger than the chorion when subjected to biaxial strength testing. The amnion but not the chorion is significantly affected by the chemical and mechanical changes during gestation and the labor process. These data will help direct future studies on the effects of clinical and molecular modulators of inflammation on membrane rupture thresholds with special emphasis on the biochemical and structural changes in the amnion.

Uniaxial stress-relaxation and stress-strain responses of human amnion.

The mechanical behavior of human amnion is examined under uniaxial tensile loading conditions. Monotonic strain-to-failure and stress-relaxation tests are described for membrane strip samples of amnion obtained by removing the chorion cell layer from specimens of whole chorioamnion. The monotonic behavior of the amnion is characterized by a large stress-free strain (approximately 10%) prior to a quadratic load-displacement response. Substantial stress relaxation behavior (ranging from 20-80%) is observed, described by a two time-constant exponential decay. The effects of the application of a topical antiseptic and of prior straining and relaxation on subsequent monotonic failure properties are examined. The results suggest that while amnion is a remarkably resilient tissue material, its mechanical behavior is typical of nonlinear viscoelastic materials, and depends strongly on its history.

Mechanical failure of human fetal membrane tissues.

Mechanical integrity of the chorioamnion membrane, and the component chorion and amnion layers, was assessed with biaxial puncture testing. Fetal membranes were obtained from term placentas following labored natural delivery or scheduled cesarean section. Preterm specimens were obtained from deliveries prior to 37 weeks gestation. Dividing and peripheral membranes were obtained from multiple gestation pregnancies. Specimens were gripped between parallel plates with circular openings and loaded with an instrumented, hand-held blunt probe until rupture occurred. Peak force was recorded and rupture sites were examined. Defects in multi-layered membranes differed in both size and shape in the individual layers. Compared with chorion and whole chorioamnion, amnion was more mechanically sensitive to different obstetrical conditions. Amnion varied in response at different physical locations within the same patient. Membrane and component puncture force data were used to calculate biaxial failure strength. Membrane stresses arising from amniotic fluid pressure were computed as a function of gestational age, and compared to membrane strength to examine the criterion for membrane failure in vivo. Possible mechanical conditions for preterm membrane rupture were examined.