@fBoyle-- Metronidazole crosses the placenta and enters the fetus, so it should not be used during the first trimester. It's acceptable to use it in the second or third trimester if there is a serious infection like bacterial vaginosis or trichomoniasis. If the infection is not serious, it's better to wait until after birth or use an alternative antibiotic that's safe during pregnancy.
I agree with the article however that each case has to be considered individually. If the infection is serious and spreading and if metroidazole is the best medication for it, then it should be used. The doctor needs to make this judgement.