RESULTS
Among the 1897 LP births, 302 (16.2%) occurred at 34 weeks’, 504 (27%) at 35 weeks’ and 1061 (56.8%) at 36 weeks’ gestation. Spontaneous preterm labor accounted for 686 (36.7%) deliveries, pPROM for 398 (21.3%), while 783 (42%) were indicated LP births.
Table 1 summarizes the maternal and obstetrics characteristics of the study population presented by gestational age at delivery. Demographic features, socioeconomic attributes, medical complications (hypertensive and liver disorders, chorioamnionitis), prophylaxis with ASA or LMWH were similar across different gestational age groups. Only 4 patients developed pPROM < 34 weeks’ gestation. Diabetes mellitus was more common among mothers who delivered at 34 weeks’ gestation (p < 0.01), pPROM was more prevalent among pregnancies resulting in 36 weeks deliveries (p = 0.03), while vaginal bleeding due to abruption or abnormal placentation was less frequent among gestations leading to 36 weeks as opposed to earlier births (p < 0.01). Antenatal corticosteroids and progesterone prophylaxes progressively decreased with gestational age (p < 0.01). The last (and for 605/634 the only course) of antenatal corticosteroids was administered to 237 (37.4%) patients < 34 weeks’ gestation, while 397 (62.6%) received the treatment later. Induction of labor was more common later in pregnancy, as opposed to CDs performed prior to labor onset (p < 0.01); the vaginal delivery rate increased with gestational age at delivery (p < 0.01).
Thirty-four women (4%) were diagnosed with pPROM prior to 34 weeks’ gestation, while 809 (96%) later. The median interval from rupture of membranes to delivery was 4 days (95%CI 2 -5 days). Antibiotic treatment was administered to 699 (83%) women with pPROM; although details about the duration of treatment were available for only 634 women, the vast majority (i.e. 610, 96%) received a ≤ 7 day-course.
Fetal characteristics are displayed in table 1. Non reassuring fetal status, prenatally diagnosed fetal anomalies, and amniotic fluid abnormalities were similar among study groups, while IUGR was significantly less common when delivery occurred closer to term (p < 0.01). Circumstances at parturition (spontaneous PTL, pPROM or indicated deliveries) did not differ according to timing of delivery (Table 2). Instead, most neonatal outcomes were affected by gestational age (Table 3). No cases of neonatal deaths were detected in our study population. The prevalence of metabolic acidosis and respiratory support dropped with gestational age at delivery (p < 0.01), while 5’ Apgar score and cardiopulmonary resuscitation remained unaffected (Table 3). Later deliveries were associated with higher birthweights, higher proportions of SGA infants, as well as lower rates of jaundice, difficulty feeding, hypoglycemia and sepsis (p < 0.01).
The composite neonatal outcome was detected among 27.1% (82/302) of the 34 weeks deliveries, 17.7% (89/504) of the 35 weeks deliveries, and 8% (85/1061) of the 36 weeks births (p < 0.01). Similarly, the composite outcomes respectively summarizing metabolic complications, and respiratory support decreased when delivery occurred closer to term, while the risk of metabolic acidosis and/or neonatal resuscitation was unaffected by timing of delivery (Table 3).
Multivariate analysis showed that gestational age at delivery had the most significant impact on the composite neonatal outcome, metabolic complications, and the need for respiratory support. Table 4 summarizes the multivariate logistic regression models investigating the role of timing and circumstances at delivery. Neonatal morbidities decreased with gestational age at delivery (p < 0.01), and were associated with indicated births (p < 0.01); of note, outcomes of pregnancies delivered due to pPROM were similar to spontaneous PTLs (Table 4). Instead, timing of delivery did not affect neonatal resuscitation, that appeared to be uniquely associated to deliveries indicated by maternal, fetal or obstetric complications (p < 0.01). Table 5 illustrates the multivariate logistic regression models assessing the impact of maternal medical conditions, fetal characteristics, pregnancy complications, and gestational age at delivery on neonatal morbidities. As gestational age increased, the composite neonatal outcome, metabolic complications and the need for respiratory support dropped (p < 0.01). Considering the same outcome measures, pregestational diabetes was a significant risk factor for neonatal morbidities (p =0.02, < 0.01, and < 0.01 respectively), while preeclampsia showed a protective effect (p =0.03, < 0.01, and 0.04 respectively). Vaginal bleeding due to abruption or abnormal placentation (p = 0.03), increasing maternal BMI (p = 0.03, and 0.02 respectively), and polyhydramnios (p = 0.045, and < 0.01 respectively) were significantly associated with both the composite neonatal outcome and respiratory support, while pPROM (p < 0.01) was solely associated with the composite neonatal outcome. Non-reassuring fetal status was related to both metabolic complications (p < 0.01), and respiratory support (p = 0.04); instead, spontaneous PTL (p < 0.01) had a protective effect on the risk of metabolic complications, as opposed to IUGR (p < 0.01). Gestational age at delivery did not affect the risk of metabolic acidosis and/or neonatal resuscitation; the likelihood of such outcome was associated with bleeding due to placental abruption or abnormal placentation (p < 0.01), as well as with non-reassuring fetal status (p < 0.01).