Do differences in Toxoplasma prevalence influence global variation in secondary sex ratio? Preliminary ecological regression study.
OBJECTIVE RhD-positive subjects are protected against toxoplasmosis-associated impairment of psychomotor performance. Here we searched for RhD-positivity-associated maternal protection against the effects of toxoplasmosis. METHODS In the present retrospective cohort study, we analysed data from 785 (139 RhD-negative) Toxoplasma-free and 194 (27 RhD-negative) Toxoplasma-infected pregnant women. We searched for effects of toxoplasmosis and Rhd-phenotype on maternal weight before pregnancy, pregnancy weight gain, fetal ultrasound data (biparietal diameter, abdominal circumference, femur length) and on birth length and weight. RESULTS At pregnancy week 16, the RhD-negative mothers with toxoplasmosis gained more weight than others (P < 0.001). The difference of about 1600 g remained approximately constant from pregnancy week 16 until the end of pregnancy. Neither toxoplasmosis nor RhD phenotype had any effect on fetal bioparameter data or birth length and weight. CONCLUSION The most parsimonious explanation for the observed data is that the RhD-positive phenotype might protect infected subjects against a broad spectrum of detrimental effects of latent toxoplasmosis, including excessive gestational weight gain.