Trial aims to measure social effects of choosing babies' sex

US doctors have launched a clinical trial to assess the effects of allowing couples to select whether they will have a boy or a girl.

Doctors can use a technology called preimplantation genetic diagnosis (PGD) to examine the sex of embryos that they create by assisted reproduction. Couples then select male or female embryos to implant in the mother's uterus, but the practice is controversial and banned in a number of countries.

Sandra Carson and two colleagues at Baylor College of Medicine in Houston, Texas, started their trial last month, after nine years of consultations with their institutional review board. The doctors have a waiting list of at least 50 couples, but they will only enroll those who already have a child, and want to have a child of the opposite sex - an approach referred to as 'family balancing'.

An experimental technique called sperm sorting is currently being tested to see whether it can reliably create embryos of a desired sex. But Carson says no one has examined what happens when couples use PGD, a more established tool, to...