Fetal development begins the moment the egg is fertilized. This week your baby is the size of a poppy seed, and while this may seem small, your baby is already 10,000 times larger than they were at conception!
By four weeks of pregnancy, your baby’s development has rocketed! All of their major organs have begun to develop, and they now have arm and leg buds. In addition, your baby is no longer receiving nutrients from the yolk sac but is instead receiving their nutrients and oxygen via the placenta and umbilical cord.
The first four weeks are also when the baby’s nervous system begins to develop along with their brain and eyes. Most doctors recommend pregnant women or women trying to become pregnant take folic acid and other prenatal vitamins or supplements in preparation for their developing baby. Folic acid is known to prevent congenital disabilities, especially those related to the brain, neural tube, and spine.
You may still be confused about whether or not you're pregnant, or you may want to find out more about early pregnancy signs, symptoms and your baby's size (no bigger than a poppy seed!
This content has been adapted and updated by L. Elizabeth Forry from its original text: Pregnancy Day by Day by Consultant Editor, Paula Amato, MD (Copyright © 2008 Dorling Kindersley Limited).
You probably haven’t even taken a pregnancy test at four weeks pregnant, but your baby is already making some noticeable changes to your body. Pregnancy starts counting from the date of your last menstrual period, so you are already a month into your first trimester by week four!
It may be possible to get a positive result by pregnancy week four. Home pregnancy tests work by detecting the level of HCG or human chorionic gonadotropin hormone present in your urine. In early pregnancy, HCG rapidly increases with each day of pregnancy. While modern tests are very sensitive, don’t be discouraged if your first test comes back negative. Instead, wait a few more days and try again.
Even though you were not physically pregnant on the first day of your last period, it is the simplest and most effective way for physicians to determine your due date, and the clock starts ticking on your baby’s gestational age.
You officially become pregnant once the egg has been fertilized and becomes what is called a blastocyst. However, a fertilized egg can take several days to travel down the fallopian tube before implantation occurs, usually approximately nine days after ovulation. Once the egg has been fertilized, layers of cells begin dividing and multiplying, and the amniotic sac is formed.
If you have been keeping track of your cycles and ovulation, you can use an online due date calculator to estimate your baby’s arrival. Still, even without a positive test at this point, you could still be pregnant so let’s take a look at some of the earliest signs of pregnancy your little bundle of joy is using to show that they’re present!
The first symptom that may occur coincides with implantation. About 15-25% of women will experience implantation bleeding that looks like light bleeding or spotting. However, most women won’t have any bleeding at all or may mistake it for the beginning of their period.
Implantation bleeding is a result of the fertilized egg embedding itself into your thickening uterus. As soon as the fertilization occurs, the embryo begins dividing and multiplying cells. This sends signals to your body to produce the hormones HCG and progesterone, the pregnancy hormone. As a result, most pregnant women will get a positive pregnancy test as early as 10 days after their missed period.
Another early pregnancy symptom you may experience at four weeks is bloating and cramping. As the uterine lining becomes thicker, your belly may begin to swell. Some women also feel a cramping sensation similar to menstrual cramps.
Hormonal changes and mood swings are other early signs of pregnancy. You may notice yourself feeling fatigued and in need of a nap or a lot more sleep. The increased production of progesterone is what creates fatigue. Healthcare providers recommend naps, regular exercise, staying hydrated, and relaxing activities to combat pregnancy fatigue.
At four weeks pregnant, you may or may not be experiencing morning sickness or other digestive issues such as nausea and headaches or diarrhea. Not all women have issues with their digestive system, while others can become severely ill, as did Kate Middleton, with a condition called hyperemesis gravidarum.
Hyperemesis gravidarum is rare; only 5% of pregnant women will suffer from this disorder. However, if you are experiencing severe nausea, vomiting, diarrhea, or weight loss, speak with your OB-GYN.
Experiencing tender or sore breasts is another first sign of pregnancy gynecologists say you can watch out for. Even though it will be many months before your baby needs to eat, your hormone levels are telling your body to prepare by increasing the number of milk glands and thickening the layers of fat cells.
While it can be devasting, it is meaningful to note that 15-25% of all recognized pregnancies end miscarriage, and 80% of all miscarriages happen before the third month. Many women miscarry and go on to have healthy pregnancies. Waiting longer to take a home pregnancy test may help ease disappointment and heartache as 50% of all pregnancies end in miscarriage, many before the woman realizes she’s pregnant.
Your partner in parenting from baby name inspiration to college planning.
Subscribe