Some early signs of pregnancy include a missed period, fatigue, nausea, implantation bleeding, breast tenderness, mood swings, or no symptoms at all. Signs of a twin pregnancy could include feeling early pregnancy symptoms more intensely, but there isn’t really any way to really know you’re pregnant with twins until two babies are seen on an ultrasound. During week 4 of a twin pregnancy, blastocysts will implant in the uterine wall and form into embryos, and their body parts will begin to form. Placentas, amniotic sacs, and yolk sacs will be forming at this time to support your babies, as well.
In your 4th week of pregnancy, you may just be discovering that you’re pregnant, or you might not know for sure yet – and you may or may not be experiencing early pregnancy symptoms. While it's possible you’re noticing early pregnancy signs, such as implantation bleeding or breast tenderness, you might not have any clues for a few weeks – and that’s okay! You may have a positive pregnancy test this week, although it’s still early enough for a false negative. If you do have a positive pregnancy test and are pregnant with twins, you won’t know there are two babies until your provider sees two on ultrasound.
Symptoms of a twin pregnancy at 4 weeks are the same as symptoms of a single pregnancy would be. You may experience very early signs of pregnancy, but again, some women don’t experience any at this point. Some symptoms, such as nausea and breast tenderness may be even more intense with a twin pregnancy than with a single pregnancy, if felt this early at all. Some women have reported "having a feeling," or "just knowing" they were pregnant with twins, although this certainly isn’t the case for everyone. While intense symptoms and intuition could be signs of a twin pregnancy, the only sure way to confirm a twin pregnancy is later on by ultrasound.
Some potential early pregnancy symptoms include:
. No symptoms. Because 4 weeks is still so early in the pregnancy, many women experience no symptoms and don’t know they’re pregnant yet. If you don’t have regular periods, you may not be thinking about a missed period, or might just think it’s late.
. Missed period. Many women are tipped off to being pregnant by a missed period. A period could be late for other reasons, but a missed period is a good reason to take a pregnancy test.
. Fatigue. As your body begins to support a pregnancy and you experience an increase in the hormone progesterone, you may start feeling pregnancy fatigue.
. Nausea and/or vomiting. Many women experience pregnancy nausea, which typically starts between 4 and 8 weeks of pregnancy. Nausea is sometimes, not always, accompanied by vomiting. This pregnancy nausea is likely due to the production of the hormone HCG (human chorionic gonadotropin) in your body, along with a rise in the hormone estrogen. Even though it’s often called "morning sickness," pregnancy nausea can hit at any time of the day.
Sipping on fluids and eating smaller portions more frequently, eating bland foods, and eating crackers or something plain before getting too hungry, can help minimize the nausea.
. Implantation bleeding. Implantation bleeding happens (but not always) when the fertilized egg implants in the lining of your uterus. It's usually a light spotting that occurs one to two weeks after fertilization. Pregnant women do not always experience implantation bleeding, so don’t worry if you don’t notice any. You may also experience implantation cramping. Implantation bleeding is typically much lighter than a period and doesn't last as long.
. Breast tenderness. Breast tenderness, swelling, and soreness is an early pregnancy sign, due to a rise in hormones. You might experience other changes to your breasts as well. For instance, your areolas, which are the areas around your nipples, may darken.
. Mood swings. Mood swings can be an early sign of pregnancy, too. As with other pregnancy symptoms, this is due to an increase in hormones. You may experience periods of happiness, then sadness or anger. Or, you may notice your feelings are heightened and more intense. While mood swings with pregnancy or any hormonal changes are normal, don’t hesitate to get professional help if you believe you're struggling with depression or anxiety.
This week, your babies (at the beginning stage of blastocysts) will implant into your uterine wall and develop into embryos. The placenta, amniotic sac, and yolk sac will begin developing to support your babies.
Your twins begin with two fertilized eggs. Identical twins develop when one fertilized egg splits into two separate fertilized eggs, which each become an embryo. Fraternal twins develop when two different eggs are fertilized by two different sperm cells and each become an embryo.
Each fertilized egg will develop into a ball of cells that are rapidly dividing into more cells. These collections of cells are called blastocysts and will soon be forming into embryos, and into membranes that will support the embryos.
Weeks from now (around week 8), the embryos will be fetuses. This week, the blastocysts implant into the lining of your uterus.
This week, the inner layer of the blastocysts will develop into the embryos, and the outer layers, which are buried in the wall of the uterus, will form into the placentas. The embryos consist of three distinct layers of cells and each of these layers will eventually develop into different body systems and parts.
In the next few weeks, your baby's cells will multiply and differentiate to have specific functions. Your twin babies' brains, spinal cords, hearts, and gastrointestinal tracts will all begin to develop. Their arms and legs will start to grow from buds and their facial features will start to form. Their hearts will begin to pump and lungs will begin to develop.
In a twin pregnancy, it’s most likely that each baby will have their own placenta and their own amniotic sac. However, sometimes twin fetuses may share a placenta. In even rarer instances, twin fetuses share one placenta and one amniotic sac. If your pregnancy is one of the latter two scenarios, your provider will closely monitor your pregnancy for any complications.
The amniotic sacs will develop from the rest of the blastocysts (the remaining thin layer) and the amniotic sacs will grow to surround the embryos and will eventually fill with amniotic fluid, which the fetuses will float in.
The yolk sac is an early pregnancy structure within the amniotic sac. A yolk sac is attached to the embryo and acts as the primary source of nourishment until the placenta further develops and takes over.