Length of pregnancy in African Americans: Validation of a new predictive rule

This study evaluated whether a new predictive rule is more accurate for est imating the length of pregnancy in African Americans than Nagele's rule, th e accepted standard. After identifying women in early pregnancy, telephone interviews were conducted to obtain information about 16 previously establi shed determinants of gestational length. Based on these data, a linear mult ivariate regression model was used to predict an estimated delivery date (E DD) for each mother. In addition, the EDD was determined using Nagele's rul e. Later, the actual delivery date was compared with the EDD predicted by t he new rule and with the EDD predicted by Nagele's rule. Each pregnancy was assigned to its better prediction group, either the new rule's group or th e Nagele's rule group. Fifty-seven pregnancies were identified prospectively and monitored. The ne w rule predicted the actual delivery date more accurately in 66% (37/56) of pregnancies, Nagele's rule was a better predictor in 34% (19/56) of pregna ncies, and both rules were equally accurate in predicting the delivery date for one pregnancy. The new rule was more precise than Nagele's rule (P=.02 2) when the binomial distribution was used. When using the linear regressio n model rule, a more accurate EDD can be determined for African-American wo men. Moreover, it is possible to predict the risk of preterm delivery (thos e occurring >3 weeks earlier than the EDD).