Does mthfr heterozygous c677t mutation affect pregnancy?

Likely not much: The existing evidence does not support any strong connection between heterozygotes for either the c or a mutations of mthfr and poor pregnancy outcomes. Homozygotes may well be at greater risk. Depending on clinical history, different levels or surveillance and possible intervention can be considered.

No: It really should not. In fact that is really an old test which is not really tested for very often. It affects a hormone pathway and homocysteine is something that can build up. So mthfr really is not very useful. And being heterozygous is almost never harmful.

No: Screening everybody for polymorphisms at this locus has been promoted by a big-money lab. The test is pricey and not standard, but lawyer-shy physicians may feel they need to test everybody. A majority of women are told they have a health problem. I believe this is unfortunate and that real mthfr disease is extremely rare.