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First Trimester

The first trimester covers the first three months, from conception to the 13th week. During this time, Mum’s body needs to make significant adjustments to accommodate the pregnancy as the baby goes from a simple ball of cells to having all essential organs and structures.

Things to do after (and before) you get pregnant

  1. Stop smoking and avoid exposure to potentially harmful substances, including alcohol, drugs and chemicals, including paracetamol, as it alters male sexual development
  2. Eat and drink to nourish the baby, but not too much, and reducing sugar lessens the chances of gestational diabetes
  3. Sleep is essential to cope with the significant changes in the mother’s physical, hormonal and immune systems in the first trimester
  4. Reduce physical or mental stress levels, especially heavy lifting or getting cold and damp if possible
  5. Contact your MD/GP at least two weeks before the date of the usual first scheduled scan

Information for the first consultation

  1. The date of the last period and the usual length of your cycles
  2. The date of the positive pregnancy test
  3. Have you been pregnant before; if so, bring the details along
  4. The details of recent blood serum tests (particularly the hCG level)
  5. The pregnancy symptoms that you’ve experienced
  6. Information on current or recent medication or other drugs

Early pregnancy ultrasound

A scan at 6 or 7 weeks has the advantage of confirming the site of the pregnancy at an early date and ruling out the possibility of an ectopic pregnancy. In many (but not all) countries, this is the norm, and in fertility clinics where the risks of this happening are slightly higher.

During the first trimester (weeks 1 -12), the embryo:

  • It grows from a few cells to a baby that has all its internal organs
  • The brain is similar to how it will be at birth
  • The bones start to harden
  • By the end of the first trimester, the fetus reaches about 3½ inches (9 cm) long

The mother’s immune system has to make significant changes to accept the pregnancy, plus alterations to the blood supply and anatomy of the lower abdomen (which takes a lot of energy), so it’s normal for her to feel very tired.




The ‘blastocyst’ ball of cells that implants in the fluffy, sticky nutrient-rich lining of the womb is just 0.1-0.2 mm.

  • The placenta and the umbilical cord are forming by the third week (from your last period)
  • By the end of the first month, the baby has grown to ¼” (6-7 mm) long


  • She’ll usually be tired and sleepy a lot of the time. Her body has to make great immune, structural and hormonal changes
  • It’s normal for her to need to visit the bathroom more often
  • Feelings of nausea, vomiting, heartburn, indigestion, bloating, food aversions or cravings are common
  • She may get changes to her breasts, as well as generally feel pre-menstrual
  • Emotionally it can be tough, with extreme swings from joy and delight to misgivings and fear


  • Give up smoking, alcohol and coffee
  • An ultrasound scan at 6 to 7 weeks will confirm the baby is in the correct place, eliminate the possibility of an ectopic pregnancy, generally settle the emotions and make it all more real



  • The baby develops very rapidly in the second month, and by the end of week six, the baby has a head, body and limbs
  • All of the baby’s major organs and body systems, such as the brain, lungs, liver and stomach, are developing
  • The baby’s heart is beating by the sixth or seventh week and is visible with ultrasound. It beats slowly early in the pregnancy
  • The spinal cord is fully formed by week 7, and the limbs are growing
  • The baby reaches 8-11 mm long


  • It’s normal for twinges and aches in the lower abdomen, and about 1/3rd of women have some spotting as the uterus stretches and some old endometrium is shed
  • Feeling very tired, faint or dizzy is standard, often with headaches
  • It’s normal to be visiting the bathroom a lot, but constipation is also possible
  • Too much saliva, nausea, and vomiting (at any time of the day) are common issues this month
  • Food aversions or cravings, heartburn, indigestion, flatulence or bloating are other possibilities!
  • Breasts can sometimes feel full and sore


  • Avoid drugs, pesticides, chemicals and radiation if possible, and bacteria and viruses as some of these (such as Rubella) can harm the baby
  • It’s essential to rest when she needs to
  • Eating and drinking nourishing foods and appropriate levels of supplements (too much will be harmful) is a good idea
  • An ultrasound scan at 6-7 weeks is recommended



  • The baby is entirely formed by the end of this month, and the bones are starting to harden
  • The baby is starting to move around in the womb
  • The baby’s head is about half the size of the rest of the body; its eyes are large and open (eyelids take a while longer to form), and the brain is similar to how it’ll be at birth
  • The baby’s kidneys are fully functional and drain urine into the bladder
  • The baby’s intestines have formed, but they’re outside the baby on the umbilical cord as they can’t fit inside the baby yet
  • At this stage, the baby is no longer an embryo but is now called a fetus that weighs about 14 grams (½ an ounce) and is about 9 cm (3½ inches) long!


The sense of tiredness starts to lift at the end of the first trimester for most women and is replaced by a welcome sense of calmness. This is helped by nausea, sickness and heartburn, stopping at week 14 for most mothers.


  • Contact your MD/GP by week 10 to register with a hospital or midwife to get your 12-week antenatal appointment
  • At the 12-week antenatal appointment, they check:
    • Mum’s weight and blood pressure
    • Sugar and protein levels in your urine
    • Blood group, rhesus status and risk of diabetes
    • Baby’s growth and development and due date
  • If you want to, this is the time to test for chromosomal abnormalities:
      • Chorionic Villus Sampling (CVS) is possible at 11-13 weeks
      • Amniocentesis is possible at 15-20 weeks

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