I've just been doing some reading on routine second trimester ultrasounds from the Society of Obstetricians and Gynecologists (SOGC) guidelines (i.e. when they should be done and what they are looking for). Contrary to the Royal College of Obstetricians and Gynecologists who believe the scan should be performed between 20 and 23 weeks, the SOGC recommends doing the ultrasound between 18 and 22 weeks for best results. This scan is used to detect abnormalities related to fetal development (anatomy/size), the mother's anatomy (pelvis/bladder) and the location of the placenta (see SOGC guidelines for details). Research has shown that early detection leads to improved outcomes for mum and baby due to the opportunity for early termination or specialized prenatal care.
It has been suggested that the detection of the baby's sex be postponed from 20 to 30 weeks to avoid termination of females. An editorial recently published in the Canadian Medical Association Journal reported Canada “a haven for parents who would terminate female fetuses because they want sons [due to] developments in easy access to abortion and advances in prenatal sex determination". The article also mentions that although there are federal laws that ban sex-selection through in-vitro fertilization, this does not "protect the resulting fetus from subsequent termination on the basis of sex" (see article for more information). The SOGC does not agree that this is an appropriate way to avoid these abortions, stating that they "do not believe that the value a family places on a female child can be addressed by withholding information" (see SOGC's position statement for details).
Ultrasound is generally viewed as a safe procedure and there is no conclusive evidence (to my knowledge) that states otherwise. However, health care providers tend to limit it's use due to either the unnecessary cost and/or potential for unknown side effects.
