Pregnancy key changes timeline22nd February 2010
The BBC has published a timeline which explains the changes a woman and her baby will undergo during pregnancy.
In Britain, a woman's pregnancy is determined from the day of her last menstrual period. This means that for up to three weeks of the first month she may not be pregnant.
When the egg has been fertilized it grows from a single cell to an embryo on its route to the uterus. Once it reaches the womb it joins itself to the lining,
Most women notice they may be pregnant when they miss their period in the fifth week.
The embryo's spinal cord and nervous system begin to grow, along with blood vessels and small 'buds' that will develop into limbs.
The heart starts to grow in week seven. In week eight the embryo is given the official status of a foetus. The eyes, brain and head are all growing by this stage.
Women are told to have a scan between 10-13 weeks to determine the date their baby is due to arrive and to find out if they are having a multiple birth.
Tests for Down's Syndrome are offered at the same time - a nuchal translucency scan and a blood test.
The foetus's umbilical cord has now completely developed and nourishes it. The danger of miscarriage decreases significantly by 12 weeks and now is the time many women tell people they are expecting a baby.
The foetus is around eight centimetres in length and has a weight of approximately 60 grams.
A pregnant woman is one third of the way into her pregnancy by week 14. On average, a pregnancy goes on for around 266 days.
By the sixteenth week the foetus has grown toenails, fingernails, eyelashes and eyebrows. In week 17 it is aware of noises from outside the womb. A scan is usually carried out during weeks 18-20 and will often show if the baby is male or female.
By the nineteenth week the foetus is now about 15-20 centimetres in length, weighs about 300g and its milk teeth have grown.
A pregnant woman has reached the half way point now and may be feeling energised. However, as the uterus presses against her diaphragm it may make her feel out of breath.
By week 22 the foetus has begun to form taste buds and it can sense touch. The skull starts to harden and the skeleton carries on growing.
A scan in week 24 checks what position the baby is in. If the baby is born prematurely it could live with medical support, although it would be vulnerable to infection and could have breathing problems.
Pre-eclampsia becomes a danger by week 25 and there is a routine check for it in week 28. By week 27 the foetus's length is around 34 centimetres and it weighs around 800g.
The mother may begin to experience Braxton Hicks contractions around this time, which are painless 'practice' contractions.
By week 31 the foetus can look around and is able to distinguish light from dark. The woman's breasts begin to make colostrum, a high calorie milk, around this time.
In week 32 the mother usually has another antenatal check-up. The foetus is around 42 centimetres in length and weighs 2.2kg. If the baby is born at this time it has a good possibility of surviving.
In week 33 the baby should move into a position with its head facing downwards and by week 36 the baby's head can 'engage in the pelvis'.
Babies born following the thirty-seventh week are known as full term.
Week 40 is when the baby should arrive and the woman's cervix softens in preparation for birth.
However, a first baby can often arrive a week later than planned. The baby will be induced if there are any problems.
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Title: Pregnancy key changes timeline
Author: Jess Laurence
Article Id: 14148
Date Added: 22nd Feb 2010