Diethylstilbestrol (DES): also harms the third generation.

Diethylstilbestrol(DES) is a synthet- ic nonsteroidal oestrogen and endo- crine disruptor that was used in the 1950s-1970s to prevent spontaneous abortion, despite its lack of proven efficacy. Millions of women worldwide took DES during pregnancy. In France, between 1951 and 1981, about 160 000 children were exposed to DES during the first trimester of their intrauterine life, and in some cases almost throughout the entire pregnancy. They are referred to as "DES daughters" and "DES sons". In 2010, in France, about 25 000 DES daughters were aged 33 to 40 years: pregnancies among these women are foreseeable until about 2020. In utero exposure to DES can have harmful effects. In particular, DES daughters have an increased risk of cancer and structural abnormalities of the uterus that can adversely affect their pregnancies. What are the consequences of tak- ing DES during pregnancy for the third generation, i.e. the children of DES children? To answer this question, we reviewed the available data in mid- 2016 using the standard Prescrire methodology. According to a retrospective study conducted in France by Réseau DES France, published in 2016, which included 4409 DES grandchildren (2228 girls and 2181 boys) and about 6000 controls, about one-quarter of DES grandchildren are born prematurely. Preterm delivery exposes neonates to serious neonatal complications, including neurosensory disorders, disabilities and increased neonatal mor- tality. The more premature the baby, the greater the risk of complications. In the Réseau DES France study, cerebral palsy was more frequent in the DES grandchildren group: 59/10 000, versus 6/10 000 in the control group. A study conducted in the United States in about 4500 DES daughters found that preterm delivery occurred at a frequency of about 26%, much higher than that reported in controls. Neonatal mortality was 8 times higher among DES grandchildren, and the risk of stillbirth was twice as high. Other smaller studies have also shown an increased risk of preterm birth. A cohort study conducted in about 5000 DES grandchildren found that the risk of malformations of any type was higher than in the unexposed control group. Epidemiological studies, conduct- ed in several countries, found an increased frequency of hypospadias in DES grandsons. The relative risk was about 5 in the largest study. Other, less robust studies found no statistically significant difference. Several studies in several countries have shown a twofold increase in the risk of oesophageal atresia or tracheo- oesophageal fistula in DES grandchildren. The data on congenital heart defects or musculoskeletal malformations are limited and uninformative. Epidemiological studies have not identified a significant increase in the risk of gynaecological anomalies or cancers in DES granddaughters. Limited data are available on the risk of malformations in the children of DES sons. The data obtained in rodents exposed to DES (and other endocrine disruptors) make it entirely plausible that in utero exposure to DES, in humans too, provokes epigenetic effects that are passed on to future generations not directly exposed to DES. In practice, these data should be discussed with DES daughters, their partners and healthcare teams so that appropriate monitoring, clinical man- agement and follow-up can be arranged for both mother and baby. The harms of taking DES during pregnancy last for decades and affect future generations.