The chorionic villi are fully formed by the end of this week. In one study, 100% of the transvaginal ultrasounds showed a gestational sac. The yolk sac that helps feed your baby until the placenta is fully functional is appearing as well.
By around the end of week 4, the cluster of cells finishes implanting into the womb lining and is now known as an embryo. A membrane called the amniotic sac is forming around the embryo. It is filled with a clear liquid called amniotic fluid, in which the baby floats and is cushioned.
Increasing levels of the pregnancy hormone chorionic gonadotrophin (HCG) mean that you may be starting to experience some of the signs and symptoms of pregnancy. Early signs can include feeling sick, larger or tender breasts, needing to urinate more often, and feeling more tired than usual.
Your body is figuring out what is going on! A urine pregnancy test would probably be positive by now. They measures the amounts of the pregnancy hormone, hCG, in your urine. You are probably beginning to feel tired, urinate more frequently, experience mood swings, and possibly have tender or swollen breasts – these are common signs of pregnancy.
You may also experience a change in your sense of taste and you might start craving particular foods, or suddenly dislike things such as alcohol or coffee. Don’t eat things that make you feel ill, but also don’t avoid a healthy balanced diet just because you may be feeling nauseous. Get going on a pregnancy exercise programme.