Very few studies have attempted to evaluate the risk of malformations in this population, even though it is clearly a population at risk because it is widely exposed to factors strongly thought to be implicated, such as nutritional deficiency, smoking, and use of toxic substances, including alcohol, medications and illicit drugs.

The study based on the registry of congenital malformations in California is highly informative. According to this study, which covered 1,028,255 births between 1983 and 1988 and considered only live births, women under 20 years of age had an overall risk of producing children with malformations 11 times higher than that observed for the lowest-risk women aged 25–30 years. The two ends of the curve, which had a J distribution for all abnormalities, corresponded to <15 and >45 years.

When chromosomal anomalies were excluded, the curve had a U configuration (end values of the same order of magnitude) with the same phenomenon of the highest prevalence found for the youngest and oldest age groups and the lowest prevalence for women 26–32 years old.

Analysis of the Parisian registry of malformations from 1981 to 1994 covered all the medical abortions performed after prenatal diagnosis of malformations in all Parisian facilities; 1,650 births were recorded for mothers under 18 years old. The frequency of malformations, including chromosomal anomalies, was 3.2%, while it was 2.8% for 20- to 24-year-olds and 3% for women 25–29 years old.

Concerning the pregnant teenage population in the metropolitan Paris area, the most striking are the elevated numbers of cases of anencephalies, cleft palates, polycystic kidney disease, abdominal wall-closing defects and chromosomal anomalies (especially trisomy 21). This enhanced risk of anomalies for children born to adolescent mothers should encourage heightened vigilance during ultrasonography for morphological study of the fetus because more and more of these pregnancies will affect teenagers not benefiting from favorable socioeconomic conditions, i.e., those who smoke, take illicit drugs, and have an unbalanced diet.