Your baby is still incredibly small, about the size of a poppyseed.. Your baby is implanting deeper into your uterine lining this week.
The ball of cells which make up your baby divide into two separate parts now.
One part becomes the beginning of the placenta and the other your developing baby.
The cells are multiplying rapidly and your baby now is made up of three specialized layers: the endoderm, mesoderm and ectoderm.
The endoderm is the inner layer which will later develop into the digestive and respiratory organs, including the liver and lungs.
The mesoderm is the middle layer which will soon become bones, kidneys, muscles, the sex organs and also the heart.
The ectoderm is the outer layer and will make up tissue (such as skin and hair) and organs including the nervous system.
The ectoderm also will form your baby’s umbilical cord.
By the end of this week, the amniotic sac is starting to form. It will soon be filled with amniotic fluid, which your growing baby will float in.
By the tail end of this forth week of pregnancy, the earliest visible sac can be detected by ultrasound in close to all normal pregnancies, although ultrasounds are not routinely done during the first several weeks of pregnancy.
Early ultrasounds (done during the first trimester) are done using a trans-vaginal probe which is placed directly into the vagina. This allows the transducer to get closer to your uterus and create better images, since your baby is so very tiny.
Pregnancy Week 4 – Your Body
Your menstrual period is probably expected to arrive at the end of this week, but it won’t come because of the hormones being produced now. These hormones stop your body from ridding your uterus of the endometrium and tissue in which your newly-implanted baby is burrowed in. It’s still too early in your pregnancy for you to notice any major changes. There are no obvious physical changes, but your intuition may already have you suspecting you’re pregnant. Some women claim they “just know” something is different, even though there is no solid evidence this early.
Your body may start to let you know you”re pregnant by causing you to experience a few early signs of pregnancy towards the end of the week caused by the hormones your baby is secreting, but you may just think they are signs of impending menstruation, since they can be very identical to premenstrual syndrome (PMS). Many times, a missed period is the very first hint that you may be expecting.
By the end of the week, your period may be due and a home pregnancy test could show a positive, although it”s still pretty early to rely on a test to be accurate now. Some home pregnancy tests claim they can be fairly accurate as early as 7-10 days after conception, but usually a test would show a positive until after your period is a day late (sometimes later). Human chorionic gonadotropin (hCG), which is the hormone that pregnancy tests detect, doubles every 2-3 days in a normal pregnancy. This is why the longer you hold off before taking a test, the more accurate the results will be. A negative result at this point definitely isn’t a good indicator that you’re not pregnant.
You should be avoiding any and all beverages which contain alcohol. If you consumed a couple alcoholic drinks before you were aware of your pregnancy, your baby is most likely just fine. If you’ve been trying to conceive, you probably have been steering clear of alcohol already, but if not, you need to stop drinking now. Alcohol has many major adverse effects on unborn babies, which can cause your baby to be born with severe disabilities. It interferes with your baby’s development and may lead to a serious condition called fetal alcohol syndrome (FAS).