Paternal age, placental weight and placental to birthweight ratio: a population-based study of 590,835 pregnancies

Study question: Is the age of the father associated with placental weight or the ratio of placental weight to birthweight?

Summary answer: Placental weight and placental to birthweight ratio increased according to increasing paternal age, also after adjustment for maternal age.

What is known already: High paternal age and also high placental to birthweight ratio have been associated with adverse pregnancy outcome.

Study design, size and duration: We performed a population-based study and included all singleton births after 22 weeks of gestation in the Medical Birth Registry of Norway (n = 590,835) during the years 1999-2009.

Participants/materials, setting, methods: We compared mean placental weight and placental to birthweight ratio between paternal age groups. The association of paternal age with placental weight was estimated by linear regression analyses, and adjustments were made for maternal age, birthweight, parity, offspring sex, gestational age at birth, maternal smoking, pre-eclampsia, maternal diabetes mellitus and pregnancy after assisted reproductive technology (ART).

Main results and the role of chance: In pregnancies with fathers aged 20-24 years old, the mean placental weight was 656.2 g [standard deviation (SD) 142.8], whereas it was 677.8 g (SD 160.0) in pregnancies with fathers aged 50 years or older (P < 0.001). The mean offspring birthweight in pregnancies with fathers aged 20-24 year old was 3465.0 g (SD 583.8), and it was 3498.9 g (SD 621.8) when the father was 50 years or older (P < 0.001). The placental to birthweight ratio in the corresponding paternal age groups were 0.191 (SD 0.039) and 0.196 (SD 0.044) (P < 0.001). In multivariable linear regression analysis the placentas in pregnancies fathered by a man of 50 years or older were estimated to weigh 13.99 g [95% confidence interval (CI) 10.88-17.10] more than in pregnancies with a 20-24-year-old father (P < 0.001) after adjustment for maternal age, birthweight, parity, offspring sex, gestational age at birth, maternal smoking, pre-eclampsia, maternal diabetes mellitus and pregnancy after ART.

Limitations, reasons for caution: Paternal age explains only a small proportion of the total variation in placental weight.

Wider implications of the findings: Our findings may increase the understanding of the father's role in human pregnancy.

Study funding/ competing interest(s): Norwegian Resource Centre for Women's Health, Norway. No conflict of interest.

Trial registration number: N/A.