Heinz - Tinytums

First Trimester

The first trimester is the earliest stage of pregnancy when your body undergoes massive change to establish and nurture your tiny growing baby. Here, we explain some of the important developments, which occur during this period, how to recognise the first signs of pregnancy and how to keep fit both physically and mentally.

Month one
A pregnancy is dated from the first day of your last period, which is about 2 weeks before the egg is released. Women usually release one ripe egg a month from their ovaries during their reproductive years; men make millions of sperm continuously.

When you make love and a man ejaculates, it can be as little as 20 minutes before the fastest sperm in the pack reaches the waiting egg. The special sac of enzymes it carries on its "nose" explodes on impact like a chemical warhead, dissolving a gap in the egg-shell and the sperm burrows furiously inside. Once it has got this far, changes take place on the egg membrane's surface, barring entrance to latecomers.

The sperm's genetic material now fuses with the egg's, creating 23 pairs of chromosomes which form the blueprint for all your future baby is going to be. Fertilisation has now taken place but before you can become 'properly' pregnant the cell bundle has a 3-step programme:

The single new Mother Cell needs to divide into a 64-cell bundle.
This moves down the fallopian tube to reach the womb.
It then burrows into the womb. You're now officially pregnant.

Month two
Weeks 5-6
Your pinhead-sized blob is now an embryo, and very influential despite its size, making enough of the hormone Human Chorionic Gonadotrophin (HCG) to stop you having a period and shedding your womb lining with its new occupant.

Outside it looks like a tiny bubble as the yolk sac and amniotic sac are now visible. Inside the cells for each tissue type (bones, intestines, skin) are jockeying around for position and moving into the right places for forming different parts of the body.

A stripe down the back is curling over on itself to form firstly a groove, and then a hollow tube made up of some 125,000 cells (quite a feat as the embryo only had a total of 64 cells a couple of weeks ago). This is the neural tube, which later becomes the spinal cord. At the top is the early brain area.

During the next few weeks, if you could look inside your womb, you would see the embryo fast-forwarding through man's links with his animal ancestors as it resembles in order:

A fish embryo with gills
An amphibian
A 'prototype primate'
And finally, around month 3, a perfect, if large-headed, human

Your baby has a distinct head and tail, plus budding arms and leg projections. Your baby is now a tiny (0.5mm) shrimp-like little being.

If you have a transvaginal ultrasound scan, which is sometimes done to confirm that a pregnancy is in place, your baby's heartbeat will show up as a tiny pinprick of light strobing on and off.

Weeks 7-8
Your baby has the beginnings of a face with dark eyes forming from each side of the head a mouth indentation, upper lips and nose tip appearing. The intestines are getting so long that there isn't enough room for them and they project into the umbilical cord. The tail has now almost vanished.

Your baby is jumping and startling in the womb. Sensitive ultrasound tests have found that babies begin their first movements when less than 2.5cm long.

By week 8, your baby is approximately 2.5cm long and weighs about 3g.

Month three
Weeks 11-12
Around the 12th week, you will usually be offered an early ultrasound scan. This is to check:

The placenta's position in the womb
Your baby's position
Your baby's size and probable age and possibly the sex
The thickness of skin fold (Nuchal fold) at the back of your baby's neck, which can be used as an assessment of the likelihood of your baby having Down's syndrome

Your baby is now able to hiccup, make isolated arm and leg movements instead of general 'twitches', stretch and make some chest movement.

Weeks 13-14
By week 13, your baby is capable of yawning, sucking its thumb, practising breathing movements, and moving arms and legs rhythmically, rather than jerkily as before. Fine, downy hair, called “lanugo”, is beginning to appear on your baby's body in patterns following the grain of the skin. Eyelids have now met and fused together, they will not open until month 7 of pregnancy.

By week 14, your baby is approximately 8-11.5cm long and weighs about 25g.

The end of this third month is celebration time, as your pregnancy is now more stable and miscarriage is far less likely after this point. This is partly because the placenta has taken over the production of the hormone progesterone, which is responsible for keeping the pregnancy in place.