All women in their first trimester should have an ultrasound to make sure they do not have an ectopic pregnancy.

所有在妊娠头3个月的女性都应该做超声波检查以确保没有发生异位妊娠。

youdao

So he and colleagues measured the feet of 49 women during their first trimester and again five months after childbirth.

于是他和同事测量了49位处于妊娠初期的女性的脚的尺寸，分娩后五个月再进行一次测量。

youdao

Once the first trimester is over, most women have spent a couple of months out of an exercise routine and are intimidated to start something new or resume their past exercise routine.

一旦第一阶段结束，接下来的几个月许多的准妈妈们仍然远离运动或者不敢开始新的运动或恢复以前的运动习惯。

youdao

And so we are proposing to give this pouch to mothers in their first or second trimester, when they come in for their first antenatal care visit.

VOA: special.2010.05.24

Women in their first trimester during the earthquake rated it as "extremely upsetting" whereas those who experienced it during the third trimester found it only "moderately" upsetting, she said.

BBC: Earthquakes 'trigger early births'