Total and individual triplet birth weights as a function of gestational age

OBJECTIVE: Our purpose was to determine the relationship between gestational age and both the total and individual triplet birth weights. STUDY DESIGN: A 1988-2000 prospective cohort of 3238 live-born triplets in the United States was evaluated. The mean individual (heaviest, middle, and lightest) and total triplet birth weights were correlated with gestational age in nulliparous and multiparous patients. RESULTS: The mean total triplet birth weights significantly correlated with gestational age for both nulliparous women and multiparous women, but the respective regression lines were significantly different (P =.0018). The respective regression lines for individual triplets showed a significant linear correlation (R-2 = 0.996-0.998). Interparity and intraparity differences of the individual triplets' regression lines were also significantly different. CONCLUSIONS: The relationships support a model of two distinct growth periods for triplets: an age- and growth-promoting period until 33 weeks and an age-promoting growth-restricting period thereafter.