JPED Journal

Background

The relationship between birth spacing and perinatal outcomes has been a concern of healthcare providers for a long time [13]. Years ago, the World Health Organization (WHO) endorsed a 24-month interval between the delivery (previous) and the conception of the next (subsequent) pregnancy [4]. More recently, the American College of Obstetricians and Gynecologists (ACOG) recommended women avoid an interpregnancy interval (IPI) shorter than 6 months and longer than 60 months [5].

Many early reports focused on the association of short IPI (<18 months) with a high incidence of preterm birth and low birthweight while recent work highlights a risk of severe maternal morbidities and a higher risk of infant mortality after long (≥ 60 months) IPIs [6-9]. Other studies provided limited but consistent evidence that short IPI is associated with an increased risk of obesity and gestational diabetes (GDM) in the subsequent pregnancy [6,10].

Obesity is the most common medical condition that affects women of reproductive age globally [11-12]. Obesity before and during pregnancy are major risk factors for pregnancy loss, gestational diabetes mellitus (GDM) and pregestational diabetes mellitus (PGDM), hypertensive conditions, labour complications and severe maternal morbidities [11-14].

The benefits of lactation on short and long term maternal and infant health have been clearly documented [15-17]. Exclusive BF or any BF during birth hospitalization and through the first postpartum year are important for healthy women and for those with severe maternal comorbidities including obesity, chronic hypertension (CHTN), preeclampsia, GDM and PGDM that may interfere or delay BF initiation or BF duration [17-21]. Despite numerous publications on birth spacing and perinatal outcomes, associations between IPI, obesity and BF among sibships remain underreported [3,6,22].

Objective

The main objective was to estimate differences of IPIs stratified by short (< 18 months), intermediate (18-59 months) or long (≥ 60 months) with comorbidities and intention to BF by women with Class 3 obesity and infant feeding [exclusive BF (EBF), formula feeding (FF) or partial BF (BF/FF)] at discharge [4,5].

Subject and Methods

This retrospective cohort investigation was approved by the Biomedical Sciences Institutional Review Board at The Ohio State University [IRB 2024H0198]. Electronic maternal and neonatal records (2013-21) were reviewed. In agreement with the WHO and the ACOG, we categorized women with Class 1 (29-34 kg/m²), Class 2 (35-39 kg/m²) and Class 3 obesity (low 40-49 kg/m² and high ≥ 50 kg/m²) [4-5,22]. The study included women with Class 3 obesity who delivered at ≥ 34 weeks a first and second singleton live birth without major malformations. Advanced maternal age is defined as ≥ 35 years at delivery. Women with GDM, PGDM, CHTN, preeclampsia, anemia, polycystic ovary syndrome (PCOS), obstructive sleep apnea (OSA) and gastroesophageal reflux disease (GERD) were diagnosed and treated following established guidelines [5,23-26]. Infants born between 34 and 36 6/7 weeks of gestation were considered late preterm. Gestational weight gain (GWG) was defined as adequate, inadequate or excessive [27]. According to gestational age (GA) and birthweight, infants were categorized as small (SGA), appropriate (AGA), or large (LGA); those with birthweights ≥ 4000 g were considered macrosomic [28-29]. During the prenatal visit, on arrival to labor and delivery, and shortly after birth, women declared their past BF experience, if any, and their intended infant feeding choice (EBF, FF or BF/ FF) [20,30].

IPI was calculated as the time in months elapsed between the delivery of the first live birth (previous) and the start of the pregnancy that led to the next live birth (subsequent) [31]. The start of the subsequent pregnancy was estimated by subtracting the gestational age in weeks from the date of birth [1,6, 22]. As documented in the medical record, women with intervening obstetrical events such as miscarriages, ectopic pregnancies, and stillbirths between the previous and subsequent pregnancies were excluded [22,31-33].

Depending on the condition of the mother and their infant following delivery, maternal-infant interactions such as holding, skin to skin contact and BF were encouraged. Delivery room and postpartum maternal-infant interactions were observed and documented by the nursing staff [20,33].

Per our hospital practices, any symptomatic infants regardless of the mothers’ clinical condition, were directly transferred from the delivery room to the Neonatal Intensive Care Unit (NICU). Our family-centered care system has rooming-in available and fulltime lactation consultants whose services are offered to all women regardless of their infant feeding preference [20,33].

Screening for hypoglycemia (blood glucose < 40 mg/dl during the first 4 hours of life and < 45 mg/dl between four and twenty four hours of life) was done via serial point of care testing (AccuChek^®) or by plasma glucose measurement in the laboratory (Beckman Coulter AU5800, Beckman Coulter Inc., Brea, CA, U.S.A.) starting within the first hour of life after the first feeding and every 2-4 hours thereafter as needed [33].  Asymptomatic infants in the Newborn Nursery with hypoglycemia were promptly BF or FF and those with recurrent hypoglycemia were treated with intravenous (IV) dextrose. On admission to the NICU, most infants were started on IV dextrose and those who were able to feed were BF or FF.

EBF was defined as direct feedings from the breast, expressed breast milk or donor human milk (DHM). Partial BF (BF/FF) was defined by direct BF, expressed breast milk or DHM supplemented with formula [20,33]. BF was considered initiated if during the 24 hours preceding hospital discharge, infants were EBF or BF/FF [20,33]. Due to the study design, information on infant feeding following discharge was not available.

Statistical analysis

Maternal and infant characteristics were summarized with count and percent for categorical variables and median interquartile ranges (IQR, 25th and 75th percentile) for continuous variables. Multinomial regression was used to estimate the association of IPI on both intention to BF and infant feeding type at discharge. Pregnancy, delivery and infant complications may be related to BF and occasionally may be confounders for the association of IPI on BF. These associations were explored with descriptive statistics [34-36].

Following best statistical practice and STROBE reporting guidelines, p-values are not presented in descriptive tables [3436]. For the main analyses, estimates and 95% CI intervals are presented, and the p-values are interpreted on a continuum with smaller p-values supporting evidence that the data are incompatible with the null hypothesis. All analyses were performed using R version 4.4.0 [37].

Results

Short IPI compared to intermediate IPI

Demographic and clinical maternal characteristics such as severe obesity, median age, advanced maternal age, white, African American, public healthcare assistance, current smokers, former smokers, GDM A1 and A2 combined, PGDM Type 1 and 2, CHTN on anti-hypertension medication, severe preeclampsia, vaginal delivery, primary and repeat cesarean, median pregestational weight, median weight at delivery and excessive gestational weight gain were similar between short and intermediate IPI (Table 1).

Neonatal outcomes of short vs intermediate IPI were similar in median GA, late preterm, median birth weight, admission to NICU and neonatal hypoglycemia (Table 2). However, infants in the short IPI have a higher prevalence of LGA (31 vs 17%) and macrosomia (24 vs 12%).

Table 1: Maternal and Clinical Demographics According to Interpregnancy Intervals.

Table 2: Neonatal Outcomes According to Interpregnancy Intervals.

Long IPI compared to intermediate IPI

Women in the long IPI group tend to be older (31 vs 29y), of advanced maternal age (30 vs 13%), on public healthcare assistance (70 vs 55%), current smokers (15 vs 6%) and have CHTN on medication (21 vs 6%) (Table 1). Among dyads in the long IPI, vaginal delivery rate was lower (36 vs 48%) while A2 DM (17 vs 6%), median pregestational weight (129 vs 115kg) and weight at delivery (140 vs 126kg) were higher. The prevalence of low and high BMI in Class 3 obesity was similar. Compared to the intermediate group, newborns in the long IPI had similar rates of AGA, SGA, LGA and macrosomia (Table 2). Neonatal hypoglycemia (29 vs 16%) was higher in the long IPI group whereas admission to the NICU (19 vs 13%) was similar.

Intention to breastfeed and infant feeding at discharge

Intention to BF (73, 68 vs 55%) was lower and, consequently, intention to FF (19, 21 vs 27%) was higher in the long IPI as compared to the short and intermediate IPI groups (Table 2). At the time of discharge from the hospital, EBF rates were similar for the short and intermediate groups but were lower in the long IPI group (38, 36 vs 21%). While the rates of BF/FF were comparable (26, 30 vs 26%), those of FF only were higher in the long IPI group (36, 34 vs 52%).  

From the multinomial regression models, estimated probabilities are shown below in Figure 1. Across all IPI, intention to EBF was higher than intention to FF or partial BF. At discharge, the distribution of feeding for short and intermediate IPI were similar, whereas long IPI had higher rates of FF as compared to BF/FF.

Figure 1: Estimated probabilities and 95% confidence intervals of Intention to Breastfeed (A) and Infant Feeding at Discharge (B) from multinomial logistic regression models.

The odds for intention to FF compared to EBF were lower for short vs intermediate IPI (aOR: 0.83 (95% CI 0.43, 1.58, p = 0.6)), but higher for long vs intermediate IPI (aOR: 1.59 (95% CI 0.84, 2.99, p = 0.2)). However, these estimates have wide confidence intervals. At discharge, the odds of FF vs EBF were higher for long compared to intermediate IPI (aOR: 2.53 (95% CI 1.31, 4.91, p = 0.006)).

Breastfeeding initiation

BF initiation (EBF and BF/FF combined) was observed in 64% of the short, 66% of the intermediate and 48% of women in the long IPI group. The rate of women who were unable to BF exclusively or partially during their hospitalization was similar for those in the short and intermediate groups (24 vs 26%), but it was higher (39%) for those in the long IPI group. Prior BF experience was more common among women in the intermediate and short IPI than those in the long IPI group (Table 2). Lactation assistance, regardless of the IPI, was provided to a similar number of women.

Breastfeeding experience of the previous pregnancies

A review of the 191 women with prior BF experience with that of 148 without prior BF experience showed clinical and demographic similarities except for the lower prevalence of public healthcare assistance (52 vs 70%) and current smoking (6 vs 14%) (Table 3). Additionally, prior BF experience was similar in the short IPI, more common in the intermediate (51 vs 43%) and less frequent in the long IPI (20 vs 30%). Among women with prior BF experience, their prenatal choice of infant feeding for the subsequent pregnancy was: 87% intended to BF, 12% intended partial BF, while 1% intended to FF only. In contrast, of the women with no prior BF experience, 39% intended to EBF, 13% intended BF/FF and 49% intended FF. Consequently, at discharge, women with prior BF showed higher rates of exclusive BF (45% vs 17%), BF/FF (34 vs 22%), BF initiation (79 vs 39%) and lower rates of FF (21 vs 61%).

Table 3: Neonatal Outcomes Including Breastfeeding in the Subsequent Pregnancy