Maternal characteristics of the undocumented women were significantly different from the population as a whole (Table ). Undocumented women were more likely to be between 17 and 35 years of age (93% v 87%, p < .001), less likely to have finished high school, and more likely to be unmarried than their counterparts in the general population.
Maternal and pregnancy characteristics, Colorado singleton births, 1998–1999
Behavioral characteristics were also significantly different for the two groups. The undocumented women were far less likely to smoke (1.9 % v 11.1 %, p < .001). However, the undocumented women were less likely to have gained an adequate amount of weight during their pregnancy (23.5 % v 12.7 %, p < .001), and were less likely to receive an adequate number of prenatal care visits (47.3% v 20.1%, p < .001).
Undocumented women were less likely to have a primary (first time) C-section than other women in the population, and more likely to have a vaginal birth after C-section (Table ). Undocumented women also experienced more complications of labor and delivery. They were significantly more likely to have meconium staining, excessive bleeding, precipitous labor, breech presentation, cord prolapse, and fetal distress (p < 0.01).
Labor and delivery methods and complications; Colorado singleton births, 1998–1999
The difference in mean birth weights was not clinically significant (Table ). Undocumented women were significantly less likely to deliver a low birth weight infant (6.5% general population v 5.3% for undocumented women, p < 0. 001). The mean gestational age was slightly higher for the infants of undocumented women (39.1 weeks v. 38.9 weeks, p < .001). This difference is likely not clinically significant. However, the rate of preterm births was significantly lower among the undocumented group (12.9% v 14.5%, p < .001).
Birth outcomes, Colorado singleton births, 1998–1999
All abnormal conditions of the newborn (infant anemia, birth injury, fetal alcohol syndrome, hyaline membrane disease, seizures, and requirements for assisted ventilation) were collapsed into one category due to small numbers in individual cells. However, undocumented women showed significantly higher percentages than the general population in this combined category (10.0% v. 7.8%, p < .001). We did not find an increased rate of neural tube defects among infants of undocumented women in Colorado.
The Mantel-Haenzel test was used to assess the association of low birth weight and preterm birth with undocumented status, while individually controlling for the effects of smoking status, maternal age, or inadequate weight gain. The Breslow-Day test of the homogeneity of the odds ratio was not significant for any of the three analyses, and the common relative risk was estimated from the common odds ratio given by the Mantel-Haenzel test. Undocumented women were less likely to deliver a low birth weight infant even after controlling for smoking status (RR = 0.88, CI 0.79–0.99), weight gain (RR = 0.71, CI 0.63–0.80), and age (RR = 0.81, CI 0.72–0.90). Undocumented women were less likely to have preterm delivery even after controlling for smoking status (RR = 0.91, C.I. 0.85–0.98), weight gain (RR = 0.81, C.I. 0.75–0.87), and age (RR = 0.89, C.I. 0.84–0.96).