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The Second Trimester- Weeks 15 to 28

Second trimester of pregnancy

What is happening?

The second trimester is a period of rapid growth for your baby. By 18 weeks of pregnancy the baby will weigh around 200gms and be approximately 14cm long. The body now grows more rapidly than the head, so the baby seems more in proportion. The legs will have also lengthened and the skeleton begins to harden. The eyes, which were more to the side of the head, will be facing forwards. The ears now clearly stand out from the head. The baby will become increasingly active, turning its head, opening and shutting its mouth and even breathing under water.

At 22 weeks of pregnancy the mother’s uterus will be just level with or above her navel and she will be finding it hard to do up her jeans. The baby can now partly defend itself against infection with its developing immune system. Head hair begins to appear around 22 weeks of pregnancy and fine hairs called lanugo will cover the body. A greasy protective material known as vernix covers the skin. This will help protect it from damage. If the baby is a boy the testes will have already begun to descend. Little girls will have now formed the 5 million ova that they will have throughout their lives.

At 26 weeks of pregnancy the baby will be around 23cm long and weigh around 820gms. The chance of survival is quite good now. Fingernails will now be present and eyes and eyelashes are usually recognisable. The baby gains a lot of weight during the next few weeks and they are increasingly better proportioned. The eyes will also reopen during this time. The baby now reacts to light and sound. Special cells in the lungs begin to secrete a substance called surfactant that helps to keep the lungs open and able to absorb oxygen. The chance of survival increases now with each subsequent week of pregnancy.

At 29 weeks of pregnancy the baby weighs over a kilogram. The chances of the baby surviving if it is born now are around 90%. Their lungs are much more prepared to breathe air and their central nervous system has now matured to a stage where it can maintain more rhythmic breathing and control body temperature. The baby may now have a good head of hair. The skin will not be as wrinkled, as fat is being laid down, smoothing the wrinkles out.

Changes in your body

Most women find the second trimester of pregnancy easier than the first as the symptoms of nausea and tiredness ease. But ligament pain and shortness of breath can make life uncomfortable. The breasts continue to enlarge and women should be fitted for a maternity bra. At around sixteen weeks onwards women may leak milk from their breasts. Their nipples become darker and more prominent, with little ducts appearing around them on the areola. Women can also now get a faint brown line up the middle of the abdomen (linea nigra) and brown areas of pigmentation on their face (chloasma). These fade away after the birth.

This is a particularly magical period for the mother as she begins to feel her baby move. The first movements, called ‘quickening,’ feel like bubbles or flutters in the uterus. Whilst the baby will have been moving for several weeks it takes longer for the movements to be felt. First time mothers will generally feel the baby’s movements a couple of weeks later (18-22 weeks) than mothers having subsequent babies (16-18 weeks).

Appointments and tests

By the second trimester you will have booked in for your antenatal care. You will be having antenatal visits every 4 to 6 weeks. At these visits your midwife or doctor will talk to you about your pregnancy and your baby’s movements and want to know how you are. They will take your blood pressure, feel your abdomen, measure the baby’s growth and listen to the baby’s heart rate at each visit.

At 18 to 20 weeks many women choose to have a routine ultrasound to detect any abnormalities and find out where the placenta is lying. You can ask about the sex of your baby during this ultrasound, but remember it is not always possible to tell. If you choose to have an amniocentesis this is done between 15 and 19 weeks.

At around 28 weeks of pregnancy another series of blood tests may done - the particular tests will depend on your individual situation (see table below). If you have a negative blood group you may be offered an injection of Anti D to counteract any antibodies that may develop. If your blood tests indicate anaemia is developing, you will be advised to take iron tablets. The best way to prevent anaemia is to eat a well balanced diet containing plenty of green, leafy vegetables and red meat.

Second Trimester Guide for Pregnant Women

Baby’s development
Weighs 200 grams (18 weeks)
Head hair appears (22 weeks)
Weighs around 800 grams with a good chance of survival (26 weeks)
Eyes reopen and light can be seen (26 weeks)
Weighs over a kilo with 90% chance of survival (29 weeks)
 
Changes in your body
Nausea eases
Increase in energy
Breasts growing (maternity bra needed)
May leak milk after 16 weeks
Feel baby move (16-22 weeks)
Gaining more weight
Ligament pain may begin
Start feeling breathless
Frequent erratic movement from the baby
 
Appointments and tests
4 to 6 weekly visits
Ultrasound 18 to 20 weeks to check for any abnormalities and location of the placenta
Amniocentesis if needed (between 15 and 19 weeks)
28 weeks blood tests for: Anaemia; antibodies (anti D injection if negative blood group); diabetes in pregnancy (if risk factors)
Dr Hannah Dahlen is the Associate Professor of Midwifery at the University of Western Sydney. She has been a midwife for more than 20 years. Hannah is also an executive member of the Australian College of Midwives, NSW Branch. She has researched women's birth experiences at home and in hospital and published extensively in this area. Hannah's website is www.hannahdahlen.com.au

Comments

2 comment(s) on this page. Add your own comment below.

Dee
Dec 5, 2011 4:01pm [ 1 ]

Hi. I am 22 weeks into my first pregnancy. At my 20 week scan i was told my placenta is low but was not given much more information and told i have nothing to worry as this is pretty common and the placenta (in most cases) will rise within the next few weeks. after looking into this and reading a bit more i must say i am still not at ease. should i be worried? is there anything i can do? what causes this? thanks for any advice. dee

Dec 6, 2011 9:10pm [ 2 ]

Hi Dee - You are correct low lying placentas are common. In around 5% off all pregnancies the placenta is found to be low lying at the 18 to 20 week ultrasound. As the pregnancy progress the bottom part of the uterus forms and the top part of the uterus moves upwards taking the placenta with it (imagine drawing a circle on a partially inflated balloon near the opening and then inflating the balloon fully - the circle ends up much higher on the balloon). At 34 to 36 weeks the bottom part of the uterus (known as the lower segment) is fully formed and the vast majority of cases the low lying placentas are out of the way.

In a small number of cases (around 0.5 %) the placenta does not move up out of the way.

There isn't anything you can do at this stage. Your midwife or doctor will recommend another ultrasound later in pregnancy to determine where the placenta is. There is a very good chance that the placenta will not cause a problem for your baby's birth.

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