3 weeks pregnant

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The start of the third week since the beginning of your last menstrual cycle (15-21 days) is the first week of your baby’s growth. If you have an average-length (28 day) menstrual cycle, your egg and your partner’s sperm will most likely fuse together to conceive your new baby on day 15. The fertilised egg, known as a zygote, then travels through your fallopian tubes and into your womb where it implants to continue its growth. Although women are unaware they are pregnant at this stage, week 3 of pregnancy is a time of rapid changes for both mum and baby.

Early in the third week of pregnancy is usually when fertilisation (the fusing of your egg and your partner’s sperm) occurs. By the end of the third week, implantation (the process by which your baby attaches to the wall of your womb where it will be protected for the remainder of your pregnancy) has begun. Some women experience implantation bleeding or spotting at this stage of early pregnancy. Miscarriage is common at three weeks pregnant but the signs of early miscarriage are very similar to a normal period and are not usually noticed. Find out more about the changes occurring in mum’s body in week 3.

Your new baby begins growing from your fertilised egg in week 3 of pregnancy. In the days after conception, your baby known as a zygote, travels from your fallopian tubes to your womb for implantation in the uterus lining (womb).

Find out more about when fertilisation takes place and what happens to create your growing baby after conception.


Week 3 of pregnancy is an important time to be healthy. Conception and implantation into your womb occur in the third week of pregnancy. At this stage, your pregnancy is vulnerable to early miscarriage so it’s important to avoid dangerous substances like alcohol and smoking, treat sexually transmitted infections which may be dangerous during pregnancy and get plenty of exercise.

Find out more about your pregnancy health this week.


A quick summary of the changes to mum’s body, the baby to be, medical appointments and lifestyle information for both mum and dad.

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Key points this week.



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Date Created: June 26, 2012 Date Modified: July 3, 2018