Foot Anomaly Risk Low With Amniocentesis at 13-14 Weeks – Brief Article
Mitchel L. Zoler
PHILADELPHIA — Amniocentesis during the early second trimester did not substantially raise the risk of congenital Foot anomalies in fetuses, compared with amniocentesis done after 15 weeks of gestation.
This finding, based on a review of almost 4,500 amniocenteses done on fetuses aged 11-20 weeks in Alberta, Canada, during 1994-1997, is from the largest study so far to examine the impact of early second-trimester amniocentesis on foot malformations, according to Dr. Francois P. Bernier, director of prenatal genetic services at Alberta Children’s Hospital in Calgary, and senior researcher of the study.
“I’d like to see a study with even larger numbers, but I’m not sure it will get done,” Dr. Bernier told this newspaper.
The Alberta data set included 979 evaluable infants born following amniocentesis done from weeks 11 through 12 weeks 6 days, 2,515 infants born after amnio done in weeks 13 through 14 weeks 6 days, and 962 infants born after amnio done in weeks 15 through 19 weeks 6 days.
The incidence of congenital foot anomalies was 1.1% among those who underwent amnio between 11 and 12 weeks 6 days, 0.4% in those who underwent amnio at 13-14 weeks 6 days, and 0.1% in those who had amnio at 15 weeks or beyond, Dr. Grace Yoon reported at the annual meeting of the American Society of Human Genetics.
The incidence of anomalies following amnio at weeks 11-13 was significantly higher than when amnio was done in either of the later periods, said Dr. Yoon, a medical geneticist who works with Dr. Bernier at Alberta Children’s Hospital. The difference in the rate of anomalies associated with amnios done at 13-15 weeks and those done at 15 weeks or later was not statistically significant, she added.
The background incidence of congenital foot anomalies for all infants born in Alberta during the study period was 0.24%, she said.
Parents may prefer early second-trimester amnio over chorionic villi sampling (CVS) because CVS done at 13-15 weeks has a 1% risk of triggering a miscarriage, Dr. Bernier noted. Amnio done at the same time has a 0.5% risk of miscarriage.
In addition, CVS can occasionally give an ambiguous result because of placental mosaicism–the presence of cells in the placental tissue that do not genetically match the fetus. This type of error is avoided when fetal-cell sampling is done by amniocentesis.
The findings of this study make amniocentesis a reasonable option for patients to consider when a fetus is 13-15 weeks old, Dr. Bernier said.
Timing of Amniocentesis and Incidence
Of Congenital Foot Anomalies
Gestational Age Incidence of Anomalies
11 weeks- 1.1%
12 weeks 6 days
13 weeks- 0.4%
14 weeks 6 days
15 weeks- 0.1%
19 weeks 6 days
Source: Dr. Francois P. Bernier
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