Examining the Benefits of Early Prenatal Care Using US Birth Records

Data Source and Study Population

We used birth records data from the National Center for Health Statistics for this analysis. ¹¹ The University of Arkansas for Medical Sciences Institutional Review Board determined this study was exempt from review because all records were deidentified. The study population consisted of singleton, nulliparous live births to mothers who gave birth in the United States from January 1, 2014, through December 31, 2022. We limited the study to nulliparous mothers to reduce the potential for confounding clinical or health-related factors prior to the current pregnancy. To examine the effects of prenatal care initiation on various birth outcomes, while reducing confounding cases, we included only singleton live births that were the first birth in the total birth order and excluded births with breech presentation.

Variables and Definitions

The primary independent variable of interest was the timing of prenatal care initiation, which was calculated by using the month of initiation of prenatal care and the total number of prenatal care visits. Early prenatal care was defined as initiating care within the first 3 months of pregnancy (months 1-3), late prenatal care as initiating care at month 4 or later, and never as having never received any prenatal care.

Delivery outcomes included cesarean delivery and maternal morbidity. Cesarean delivery was dichotomized as having a cesarean delivery or not. Maternal morbidity was a binary variable defined by using the Centers for Disease Control and Prevention User Guide for the Natality Public Use File ¹² and captured whether the mother experienced a transfusion, a third- or fourth-degree perineal laceration, a uterine rupture, an unplanned hysterectomy, or intensive care unit (ICU) admission. Infant health outcomes included preterm birth, small for gestational age (SGA), low birth weight, admission to the neonatal ICU (NICU) for the newborn, abnormal conditions of the newborn (eg, assisted ventilation, surfactant, antibiotics for newborn, seizures), and no breastfeeding reported at discharge. Preterm birth was defined as birth occurring before 37 weeks of gestation. SGA was defined as birth weight lower than the 10th percentile for the given gestational age estimated by using the “growthstandards” R package.^13,14 Low birth weight was defined as recorded weight of the newborn <2500 g. We examined 1 maternal health outcome, gestational weight gain, which we coded as insufficient, healthy, or excessive depending on whether the amount of weight gain was below, within, or greater than the current Institute of Medicine–recommended ranges based on prepregnancy body mass index (BMI) (underweight: 28-40 pounds; normal: 25-35 pounds; overweight: 15-25 pounds; obesity class I-III: 11-20 pounds).

We adjusted models for birth year (2014-2022), state of residence (including Washington, DC), maternal age (continuous, in years), maternal education level (elementary [did not graduate from high school]; secondary [graduated from high school]; postsecondary [some college or higher]), maternal nativity (native to the US or not), maternal race and ethnicity, maternal partner status (married, paternity acknowledged, or neither), prepregnancy BMI (kg/m²), prepregnancy diabetes, and prepregnancy hypertension.

Statistical Analysis

The final sample included approximately 10 million total births, although the sample size for specific health outcomes varied based on the missingness of those variables in the data (range, 9 940 128 to 10 495 726).

We fit logistic regression models by using the “fixest” R package to examine the adjusted association between prenatal care initiation (early, late, or never) and each health outcome. ¹⁵ For each outcome, we estimated both the difference in relative risk (risk ratio [RR]) and the difference in absolute risk (percentage-point difference) between the 3 levels of the prenatal care variable using the “marginaleffects” R package with cluster-robust SEs for state of residence. We computed pairwise contrasts as average marginal effects evaluated at the mean of the covariates. Because the RR and risk difference are nonlinear functions of the model parameters, we used the delta method to approximate their sampling distributions, propagating the cluster-robust SEs for state of residence from the underlying model. We used the resulting SEs to construct Wald-type 99% CIs and corresponding P values for each contrast. The reference group was early prenatal care, and we made all comparisons relative to this group unless otherwise specified. Because of the large sample size, we performed all analyses with significance set at P < .01 and calculated 99% CIs.

Weight Gain During Pregnancy

Late initiation of prenatal care was associated with a higher relative risk of insufficient gestational weight gain compared with early initiation of prenatal care (RR = 1.23; 99% CI, 1.17-1.30; P < .001; Table 2). Mothers who never received prenatal care had a higher relative risk of insufficient gestational weight gain than did mothers with late initiation of prenatal care (RR = 1.47; 99% CI, 1.25-1.74; P < .001).

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Table 2.

Adjusted risk ratios and absolute risk differences for maternal and infant health outcomes by timing of prenatal care initiation among nulliparous mothers with singleton live births, United States, 2014-2022^a,b

Outcome	Risk ratio (99% CI) c	P value d	Absolute difference (99% CI), percentage points
Insufficient weight gain
Late vs early	1.23 (1.17 to 1.30)	<.001	3.12 (2.28 to 3.95)
Never vs early	1.81 (1.49 to 2.21)	<.001	10.93 (6.46 to 15.39)
Never vs late	1.47 (1.25 to 1.74)	<.001	7.81 (3.79 to 11.82)
Excessive weight gain
Late vs early	0.93 (0.91 to 0.95)	<.001	−4.04 (−5.25 to −2.83)
Never vs early	0.74 (0.68 to 0.81)	<.001	−14.23 (−18.11 to −10.34)
Never vs late	0.80 (0.74 to 0.87)	<.001	−10.18 (−13.36 to −7.01)
Preterm birth
Late vs early	1.21 (1.15 to 1.28)	<.001	1.43 (0.94 to 1.92)
Never vs early	2.26 (1.82 to 2.80)	<.001	8.39 (4.77 to 12.01)
Never vs late	1.86 (1.55 to 2.23)	<.001	6.96 (3.71 to 10.21)
Cesarean delivery
Late vs early	0.98 (0.96 to 0.99)	<.001	−0.58 (−1.00 to −0.16)
Never vs early	0.87 (0.83 to 0.91)	<.001	−3.42 (−4.46 to −2.38)
Never vs late	0.89 (0.84 to 0.93)	<.001	−2.84 (−4.00 to −1.69)
Maternal morbidity
Late vs early	0.99 (0.96 to 1.03)	.63	−0.01 (−0.06 to 0.04)
Never vs early	0.98 (0.83 to 1.17)	.78	−0.02 (−0.26 to 0.21)
Never vs late	0.99 (0.82 to 1.20)	.88	−0.02 (−0.27 to 0.24)
Low birth weight
Late vs early	0.97 (0.94 to 1.01)	.04	−0.12 (−0.26 to 0.02)
Never vs early	2.03 (1.72 to 2.40)	<.001	4.70 (3.16 to 6.25)
Never vs late	2.08 (1.80 to 2.41)	<.001	4.82 (3.38 to 6.26)
Small for gestational age
Late vs early	0.97 (0.96 to 0.99)	<.001	−0.14 (−0.21 to −0.07)
Never vs early	1.25 (1.18 to 1.32)	<.001	1.30 (0.91 to 1.70)
Never vs late	1.28 (1.20 to 1.36)	<.001	1.44 (1.02 to 1.85)
Admission to neonatal intensive care unit
Late vs early	1.02 (0.98 to 1.05)	.26	0.10 (−0.13 to 0.33)
Never vs early	1.88 (1.48 to 2.39)	<.001	5.80 (2.93 to 8.66)
Never vs late	1.85 (1.48 to 2.31)	<.001	5.70 (2.96 to 8.43)
Abnormal conditions of the newborn
Late vs early	1.02 (1.00 to 1.04)	.01	0.17 (0.01 to 0.33)
Never vs early	1.87 (1.73 to 2.02)	<.001	7.67 (6.20 to 9.14)
Never vs late	1.83 (1.69 to 1.99)	<.001	7.50 (5.99 to 9.00)
No breastfeeding by discharge
Late vs early	1.09 (1.06 to 1.13)	<.001	0.43 (0.24 to 0.62)
Never vs early	1.90 (1.53 to 2.35)	<.001	4.17 (2.36 to 5.97)
Never vs late	1.74 (1.40 to 2.15)	<.001	3.74 (1.94 to 5.54)

a

Early prenatal care was defined as initiating care within the first 3 months of pregnancy (months 1-3), late prenatal care as initiating care at month 4 or later, and never as having never received any prenatal care.

b

Data source: National Center for Health Statistics. ¹¹

c

Reference group in model entered as early prenatal care.

d

Logistic regression models with cluster-robust SEs for state of residence. Significance set at P < .01.

We observed the opposite pattern for excessive gestational weight gain, with a relative reduction in risk for mothers with a late initiation of prenatal care compared with mothers with early initiation of prenatal care (RR = 0.93; 99% CI, 0.91-0.95; P < .001; Table 2). The relative risk of excessive gestational weight gain was lower for those who never received prenatal care than for those with early initiation of care (RR = 0.74; 99% CI, 0.68-0.81; P < .001). We also found a reduction in relative risk of excessive gestational weight gain for those who never received prenatal care compared with those with late initiation of prenatal care (RR = 0.80; 99% CI, 0.74-0.87; P < .001).

Preterm Birth

Late initiation of prenatal care was significantly associated with an increased relative risk of preterm birth compared with early initiation of prenatal care (RR = 1.21; 99% CI, 1.15-1.28; P < .001; Table 2). The effect was substantially larger for mothers who never received prenatal care (RR = 2.26; 99% CI, 1.82-2.80; P < .001) compared with mothers with early initiation of prenatal care. In addition, mothers who never received prenatal care had an increased relative risk compared with mothers with late initiation of prenatal care (RR = 1.86; 99% CI, 1.55-2.23; P < .001).

Cesarean Delivery and Maternal Morbidity

Late initiation of prenatal care was associated with a slightly lower relative risk of cesarean delivery compared with early initiation of prenatal care (RR = 0.98; 99% CI, 0.96-0.99; P < .001; Table 2). Mothers who never received prenatal care had an even lower relative risk of cesarean delivery than mothers with early initiation of prenatal care (RR = 0.87; 99% CI, 0.83-0.91; P < .001). Similarly, mothers with no prenatal care had a lower relative risk of cesarean delivery than mothers with late initiation of prenatal care (RR = 0.89; 99% CI, 0.84-0.93; P < .001). However, the timing of prenatal care use was not significantly associated with maternal morbidity being reported in the birth record (P = .93).

Low Birth Weight and SGA

Mothers with late initiation of prenatal care did not have a significant increase in low birth weight than mothers with early initiation of prenatal care (Table 2). However, no prenatal care was associated with more than twice the relative risk of low birth weight compared with early initiation of prenatal care (RR = 2.03; 99% CI, 1.72-2.40; P < .001). Similarly, the relative risk of low birth weight was higher among mothers with no prenatal care than among mothers with late initiation of prenatal care (RR = 2.08; 99% CI, 1.80-2.41; P < .001).

Mothers with late initiation of prenatal care had a slightly lower relative risk of SGA than mothers with no prenatal care (RR = 0.97; 99% CI, 0.96-0.99; P < .001; Table 2). No prenatal care was associated with a higher relative risk of SGA compared with early initiation of prenatal care (RR = 1.25; 99% CI, 1.18-1.32; P < .001). Similarly, no prenatal care was associated with a higher relative risk of SGA compared with late initiation of prenatal care (RR = 1.28; 99% CI, 1.20-1.36; P < .001).

NICU Admission and Abnormal Conditions of the Newborn

We found no difference in relative risk between late and early initiation of prenatal care related to NICU admission. No prenatal care was associated with nearly twice the relative risk of NICU admission compared with early initiation of prenatal care (RR = 1.88; 99% CI, 1.48-2.39; P < .001; Table 2). Similarly, no prenatal care was associated with a higher relative risk of NICU admission compared with late initiation of prenatal care (RR = 1.83; 99% CI, 1.69-1.99; P < .001).

Late initiation of prenatal care was not associated with an increase in the relative risk of abnormal conditions of the newborn. No prenatal care (vs early initiation of prenatal care) was associated with a large increase in the relative risk of abnormal conditions of the newborn (RR = 1.87; 99% CI, 1.73-2.02; P < .001; Table 2). Compared with late initiation of prenatal care, never receiving prenatal care was associated with a higher relative risk of abnormal conditions of the newborn (RR = 1.83; 99% CI, 1.69-1.99; P < .001).

No Breastfeeding at Discharge

Late initiation of prenatal care (vs early initiation of prenatal care) was associated with a higher relative risk of no breastfeeding reported at discharge (RR = 1.09; 99% CI, 1.06-1.13; P < .001; Table 2). No prenatal care (vs early initiation of prenatal care) was associated with a significant increase in relative risk of no breastfeeding reported at discharge (RR = 1.90; 99% CI, 1.53-2.35; P < .001). Compared with mothers with late initiation of prenatal care, mothers with no prenatal care had an increased relative risk of no breastfeeding reported at discharge (RR = 1.74; 99% CI, 1.40-2.15; P < .001).

Limitations

This study had several limitations. First, the study used observational data and, therefore, did not establish causation. Second, birth record data were used for prenatal care initiation and other variables, and some have questioned the reliability of birth record data, which vary substantially depending on the variables of interest.^16,17 Although the accuracy of demographic and birth weight data from birth records is generally high, data on the early initiation of prenatal care is generally considered moderate. ¹⁸ Agreement between birth records and medical records for the derived item of first-trimester prenatal care initiation has been documented at 83%. ¹⁹ Misclassification of a categorical independent variable may bias estimates depending on the direction and pattern of error. Third, there are likely confounding variables for women who receive no prenatal care, such as sociodemographic, behavioral, and health-seeking characteristics. There are also possible constraints and confounding reasons why pregnant women receive no prenatal care. These constraints include language barriers, delayed Medicaid approval, lack of transportation, lack of paid leave, or living in maternity care deserts.^2-5 These confounding variables are not captured on the birth record and, therefore, could not be controlled for. Finally, previous studies have found that prenatal care adequacy is an important predictor of birth outcomes. Although such information was available in the current study data, this study focused on the timing of prenatal care initiation, a key component of prenatal care adequacy ²⁰ and an easily communicated recommendation.