Pregnancy First Trimester

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(Week 1-12)

Weeks 1-4 Fertilisation occurs and a ball of quickly multiplying cells embeds itself in the lining of the uterus.In the UK pregnancy is calculated from the first day of the woman's last period so for as much as three weeks of this first month she might not be actually pregnant. When fertilisation occurs the tiny mass of cells called a blastocyst at this stage embeds itself in the lining of the womb which is already thickening to support it.

Week 5 The mass of cells is developing fast and becomes an embryo. For many women the first sign of pregnancy is a missed period.Home pregnancy tests are now widely available and are considered largely reliable so the mother-to-be does not have to have her pregnancy confirmed by her GP. If a first test is negative a second one a few days later may prove positive as hormone levels in the urine rise.

An embryo at 5 weeks gestation

Week 6 The embryo officially becomes a foetus. It is about the size of a baked bean and its spine and nervous system begin to form.The foetus already has its own blood system and may be a different blood group from its mother. Blood vessels are forming in what will become the umbilical cord and tiny buds which will become limbs appear.

Week 7 Baby’s heart is beginning to develop. Morning sickness and other side effects of early pregnancy may take hold.Around this time many women find they experience the side-effects of early pregnancy including needing to urinate more often due to the expanding womb putting pressure on the bladder. You may suffer from ‘morning sickness’ which actually happens at any time of the day. You may also feel a bit weepy and irritable due to the increasing number of hormones flying around your system. All medication including supplements need to be carefully checked as the foetus is undergoing vital development in the first 12 weeks. If the woman has not told her GP or community midwife she is pregnant yet now is a good time to do so.

Week 8 It is quite common to have a first scan at this stage if the woman has had a previous miscarriage or bleeding.An early scan is often done through the vagina and is used to check the pregnancy is not ectopic. It should show up baby’s heartbeat. The nervous system is also developing rapidly especially the brain. The head gets bigger and eyes form under the skin of the face. The foetus' limbs are growing and look more like arms and legs. All internal organs are developing and becoming more complex.

Week 9 The foetus is about 5cm long with its head tucked onto its chest. It has most its major organs and eyes and ears are developing.

Week 10 A scan at 10-13 weeks is recommended to pin down the date of the pregnancy. If it is a multiple pregnancy, this should also be picked up now.

Week 11 The umbilical cord is fully formed providing nourishment and removing waste products. The foetus looks fully human now.

Week 12 By this week the threat of miscarriage is much reduced. Many women announce their pregnancy to friends and colleagues.The foetus is growing in length much more quickly by now it is about eight cm long and weighs about 60 grams. The placenta is now well formed although it's not yet doing its full job. It takes over fully in week 14. The mother is likely to have her first scan this week.

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