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1st Trimester 1-4 Weeks

1-4 Weeks


Seven days after ovulation, the fertilized egg gradually implants itself in the uterus. By the 10th day, the embryo appears. The outer layer (the ectoderm) grows into the skin, eyes, ears, teeth, brain and nervous system; the middle layer (the mesoderm), will become the heart, blood vessels, muscles and reproductive organs; while the inner layer (the endoderm), will develop into the lungs, liver, bladder and digestive system. The embryo is between 0.5mm to 4mm in length and weighs approximately 0.4g.

Pregnancy is dated from the first day of your last period, so by the end of the first month the embryo is actually only two weeks old. It is barely visible to the naked eye and weighs less than one gram. Your embryo resembles that of any mammal – it looks like a tadpole!

When the egg is implanted into the lining of your uterus, your body begins to produce a hormone called HCG (Human Chorionic Gonadotrophin) especially in the morning. HCG is responsible for pregnancy tests reading positive and is necessary for sustaining a pregnancy. It now develops into an embryo and begins to form a placenta – the vital link between mom and baby. The heart develops and begins to beat. At 4 weeks the embryo is about 4mm long and weighs less than 1g. The dividing cells are in the process of forming the various body systems (the digestive system is already under construction). The evolving neural tube, which will eventually become the central nervous system (brain and spinal cord) also starts to form.

You & Your Body

You probably feel like you have an unending case of PMS with mild cramps, sensitive breasts, bloating and crankiness. That’s the good news: you are pregnant! You may also feel fatigue and nausea. On the other hand, you may feel no different to any other time!

Common signs of pregnancy:

  • Missed menstrual period
  • Sore or tender breasts
  • Tiredness
  • Frequent urination
  • Nausea or vomiting
  • Pelvic congestion

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