Influence of the mother's preceding pregnancy on the gestation length of the current pregnancy. An immunological explanation?

Introduction. A number of epidemiological studies on various diseases have drawn attention to relationships between fetal life events, as measured by health indicators and pathological events later in life. This accounts for the renewed interest in fetal health indicators. The objective of this retrospective study is to investigate the relationship between the sex of conceptuses of the mother’s preceding pregnancies and the gestation length of the current pregnancy. Methods. A population of 7773 neonates were divided into cohorts, according to the sex of the current neonate and number and sex of the mother’s preceding pregnancies. Average gestation lengths for each cohort were measured and compared between different configurations of preceding pregnancies. Results. There a positive association between the length of gestation of the neonate and its mother’s preceding pregnancies of same sex as its own. Gestation length increases with the number of conceptuses of same sex among the preceding pregnancies. Likewise, there is a negative association between the length of gestation of the neonate and its mother’s preceding pregnancies of opposite sex to its own. Gestation length decreases with the number of conceptuses of opposite sex among the preceding pregnancies. Discussion. The results of our study are compatible with the immunological hypothesis, based on the sex-linked concepto-gravidic antigenic dissimilarity, proposed to explain the association between preceding pregnancy and fetal development. The influence of the preceding pregnancy is significant enough to be taken into account for effective management of current pregnancies as well as for efficient clinical trial analysis.