At 4 weeks pregnant, baby is smaller than a poppy seed—practically microscopic. Baby is now known as a blastocyst, a teeny ball of cells, and is busy settling into their new home (your uterus), prepping for all the crucial development that will happen over the next six weeks.
At 4 weeks pregnant, the tiny life inside you (which is technically an embryo) is implanting in your uterus, where it will grow and develop over the next 36 weeks. Along with implantation in the uterine lining, comes a rise in the pregnancy hormone hCG.
Within 24 hours after fertilization, the egg that will become your baby rapidly divides into many cells. By the eighth week of pregnancy, the embryo develops into a fetus. There are about 40 weeks to a typical pregnancy.
Four weeks into your pregnancy, your baby (now an embryo) consists of two layers of cells — the epiblast and the hypoblast. These eventually develop into all of your baby's organs and body parts. Two other structures that develop now are the amnion and the yolk sac.
The fertilized egg and your uterus are making contact this week in a process called implantation, as the blastocyst you'll one day call your baby begins to attach itself to the uterine lining.
The heart of an embryo starts beating at about week 5 of pregnancy. It may be possible to detect the heartbeat at this point using vaginal ultrasound. Throughout the pregnancy and delivery, healthcare professionals monitor the heartbeat of the fetus.
Week 4 of pregnancy
For example, a fertilised egg may have implanted in your womb just 2 weeks ago, but if the first day of your last period was 4 weeks ago, this means you're officially four weeks pregnant! Pregnancy normally lasts from 37 weeks to 42 weeks from the first day of your last period.
At 4 weeks pregnant, your baby is very tiny, as the newly implanted embryo is only about 0.04 inches long. For comparison, this is just about the size of a poppy seed!
Week 4: Implantation
The rapidly dividing ball of cells — now known as a blastocyst — has begun to burrow into the uterine lining (endometrium). This process is called implantation. Within the blastocyst, the inner group of cells will become the embryo.
At 4 weeks, the blastocyst is splitting into an embryo and placenta, and an ultrasound of your uterus will only show what looks like a tiny dot called the gestational sac, and will not show a pregnancy until it is further advanced.
What does my baby look like? Your baby, or embryo, is around 2mm long (about the size of a sesame seed). The face is starting to take shape, with a tiny nose and little eyes which stay closed until around 28 weeks. Your baby's brain and spinal cord are forming rapidly inside you.
By week 5, your baby has burrowed into the wall of your uterus. It is now called an embryo and measures about 2mm from end to end. The foundations for all of the major organs are in place. The baby is inside an amniotic sac, a bag of fluid that protects it.
At 3 weeks pregnant, you've officially conceived and are in month 1 of your pregnancy — though it will be a few weeks until you can confirm the news with a pregnancy test. This week, the tiny cluster of cells (soon to become your baby!) are rapidly growing.
Four weeks isn't “just” 4 weeks—it's just about the 1-month birthday! Yay! That's a huge milestone for both your baby and you.
Even if a home pregnancy test confirms you're pregnant, you still need to make an appointment with an Ob/Gyn. The American Pregnancy Association recommends you make an appointment with your doctor for your first prenatal visit within eight weeks of your last menstrual period (LMP).
Most OBs count pregnancy starting from the first day of your last menstrual period (LMP). (It's more accurate for doctors to estimate a due date this way.) So if you think you conceived about two weeks ago, you're probably at least four weeks pregnant—maybe even five.
The reason doctors still use the last menstrual cycle as a benchmark is because it is difficult to know exactly when the sperm fertilized the egg. So when doctors say a woman is six weeks pregnant, it typically means the embryo started developing about four weeks ago.
Your weeks of pregnancy are dated from the first day of your last period. This means that in the first 2 weeks or so, you are not actually pregnant – your body is preparing for ovulation (releasing an egg from one of your ovaries) as usual. Your "getting pregnant" timeline is: day 1: the first day of your period.
Your First Ultrasound
It's typically done between 7 and 8 weeks to verify your due date, to look for a fetal heartbeat, and to measure the length of the baby from “crown to rump.” At this ultrasound, you'll also learn whether you're having one baby, pregnant with twins, or more!
How soon can you tell you're pregnant with twins? Your doctor won't be able to tell for sure until your first trimester ultrasound, which is usually done between 6 and 9 weeks of pregnancy but can be done any time before week 14.
3. If the test result is 'Pregnant' a numerical result: "1-2", "2-3" or "3+", is also displayed indicating that conception occurred 1 to 2 weeks ago, 2 to 3 weeks ago or 3 or more weeks ago.
In a twin pregnancy, there are elevated levels of hCG, making it possible to have a very early positive result. However, home pregnancy tests won't confirm if twins are present, only the presence of hCG. It takes around 2 weeks after conception for hCG to be detected in a hCG pregnancy test.
Early pregnancy symptoms (at 4 weeks)
a missed period (often one of the first signs of pregnancy) a metallic taste in your mouth. sore breasts. nausea - also known as morning sickness, although you can experience it at any time (read about morning sickness in week 6)
This week, your baby is starting to look more like, well, a baby — your little one's head is taking shape, while the cheeks, chin and jaws are also beginning to form. In week 6 of pregnancy, you may be feeling well and truly pregnant too, thanks to symptoms like heartburn, nausea and frequent urination.