Pregnancy Calendar - Week 4
Two weeks after conception, your baby is now an embryo. Now implanted into the uterine wall, the embryo will start to split into two groups. One group will form the placenta and the other will develop into your baby. At this early stage of your pregnancy the embryo is rapidly growing, from 1.5mm at the beginning of the week to 5mm by the end of week.
The embryo consists of three different layers. The inner layer, known as the endoderm, will develop into your baby’s lungs, liver, and digestive system. The middle layer, called the mesoderm, will eventually be your baby’s bones, muscles, kidneys, sex organs, and heart. Finally, the ectoderm, or outer layer, will make up your baby’s tissues and organs such as the skin, hair, eyes, and nervous system.
Should the embryo fail to find a secure place to implant itself, the fertilized egg will pass out with your next period, which you would have been expecting at the end of this week. In many cases, this may happen without your ever having known that you were pregnant. It also also quite common; about 75% of pregnancies end within the first two weeks. In other cases, when implantation has taken place, the embryo has come loose from the uterine wall; you may experience a heavy period, sometimes lasting up to 10 days. This is a miscarriage in the most basic form. Try and avoid eating soft cheeses, pate and smoked or raw seafood. This is because many of these carry listeria, which is a bacteria that can cause fetal damage or lead to a miscarriage.
A maternal blood or urine test this week would show a positive result because the embryo is secreting human Chorionic Gonadotropin (hCG), the pregnancy hormone. Home pregnancy tests, which test for hCG in the urine, may show a positive result but are not as accurate as blood tests this early in pregnancy. Due to these new hormones, you may start to feel the first few symptoms of pregnancy, which are similar to those that you would normally be feeling when expecting your period (i.e. tender/swollen breasts, cramping, mood swings and fatigue).
Revision date: June 22, 2011
Last revised: by Tatiana Kuznetsova, D.M.D.