The mnemonic code of pregnancy

Clinical observations suggest that an uncomplicated first pregnancy reduces the risk for obstetrical complications in subsequent pregnancies. Vice versa, a prior pregnancy affected by complication increases the risk for reoccurrence. However, published evidence supporting these clinical observations along with insights into distinct immunological mediators determining the course of secondary pregnancies are still sparse.

We conducted a systematic literature research using a PubMed-based approach to identify human studies with complete information on birth weight and incidences of pregnancy complications in first and second pregnancies. We included 37 studies from initially 18.592 publications in our quantitative data analysis.

We could demonstrate that a normally progressing first pregnancy was associated with a 4.2% increased birth weight in a following pregnancy without a difference in gestational age at delivery. Furthermore, the risk for complications in a subsequent pregnancy was reduced by 35-65%. In contrast, women with a prior pregnancy affected by e.g. spontaneous abortion/miscarriage, intra-uterine growth restricted or small for gestational age baby, preeclampsia or preterm birth had a 2.2-3.2-fold increased risk to be affected again in a subsequent pregnancy.

In conclusion, our data suggest that an immune memory is mounted during primary pregnancies which either promotes the successful outcome of subsequent pregnancies or – if missing or compromised – accounts for a risk perpetuation of pregnancy complication. Experimental studies done in mice indicate that regulatory T cells - key players in mediating fetal immune tolerance during pregnancy - are functional involved in ameliorating the outcome of subsequent pregnancies.

Publication History

Article published online:
07 October 2020