Pregnancy trimesters: A guide

The typical pregnancy has three trimesters and lasts around 40 weeks from the first day of a woman’s last period. In each trimester, the fetus will meet specific developmental milestones.

While 40 weeks is the usual time frame, a full-term baby can be born as early as 37 weeks and as late as 42 weeks.

Read on for more information about what to expect during each pregnancy trimester.

Pregnancy trimester infographic <br>Image credit: Stephen Kelly, 2018</br>

Image credit: Stephen Kelly, 2018

The first trimester

The first trimester lasts for the first 12 weeks of the pregnancy and is crucial for the baby’s development. At conception, the egg and sperm combine to form a zygote, which will implant in the uterine wall.

The zygote becomes an embryo as the cells divide and grow. All of the major organs and structures begin to form.

At 4–5 weeks, the embryo is only 0.04 inches long but will grow to around 3 inches long by the end of the first trimester. The embryo is now looking a lot more like a human baby.

The fetus’s heart will start beating by the eighth week. The eyelids remain closed to protect its eyes. The fetus can also make a fist at this stage. Also, external genitalia will have formed and may be visible during an ultrasound, meaning that a doctor can tell someone whether the fetus is male or female.

A woman will experience many changes during the first trimester, too. Many women will start to feel morning sickness, or nausea and vomiting due to pregnancy, at 6–8 weeks.

Despite its name, this nausea does not just occur in the morning. Some pregnant women get sick at night, while others are sick all day.

A pregnant woman might also feel very tired and notice that she is more emotional than usual due to hormonal changes.

Many also report experiencing food cravings or aversions during early pregnancy, alongside a stronger sense of smell. Breast tenderness is also very common.

Click here for full guide.

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