Some women are already experiencing the first pregnancy symptoms, others may already suspect the little being in their belly, and still others have no idea yet that they are pregnant. Whether you’re aware of it or not: in the 4th week of pregnancy, significant developments are already taking place in your body. You can read here what exactly is changing for you and your baby this week.

How big is your baby in week 4 of pregnancy?

Your baby is now up to one millimeter in size—about the size of a poppy seed. It is still so small that, during an ultrasound, there would still be nothing to see.

4th Trimester: What's Changing for You

The implantation of the fertilized egg is complete, and from now on it is referred to as the embryo. At this stage, it still consists of two parts: the cells from which the placenta and umbilical cord will later develop ( Trophoblast ) and those from which the actual embryo develops ( Embryoblast ). This week, the amniotic sac, yolk sac, umbilical cord, and Placenta begin to form. The placental cells fuse with your uterine lining so that you and your baby are connected via fine blood vessels. However, it is still tiny and, at this stage of development, is referred to as the Chorion . To maintain the pregnancy, the placenta now begins to produce various hormones: hCG ( human chorionic gonadotropin ), estrogen, and progesterone (corpus luteum hormone). hCG is also referred to as the pregnancy hormone and prevents the shedding of the uterine lining. Progesterone relaxes the uterine muscle so that it can expand adequately in the coming months to accommodate your baby. But the rest of the body is also affected by the hormone, so you may now notice the first Pregnancy signs such as fatigue, more frequent urination , or constipation. Some women now feel a slight pulling in the lower abdomen or have tender breasts. However, it is just as possible that you are not yet aware of, or do not feel, the little being in your belly at this time—that is completely natural, too. But it won’t be long before it makes itself clearly known.

4. WEEKS: Development of Your Baby

The embryo is connected to the Chorion —the precursor of the placenta—via the umbilical cord , which is also developing. This, in turn, now connects to the inner wall of your uterus and your bloodstream via villi, and performs its important function during pregnancy by exchanging oxygen, nutrients, and waste products between your circulation and that of your child. But this is not the only important development the embryo undergoes this week: until now, all of its cells were pluripotent , which means that each cell could develop into any organ. This changes in the fourth week. The cells now begin to specialize and differentiate into three different cell layers, the so-called germ layers,
to develop further. From the outermost cell layer ( Ectoderm ) the brain, nerves, hair, nails, skin, eyes, and ears develop. From the second layer ( Mesoderm ) the basis for the skeleton, muscles, heart, and blood vessels forms. From the innermost layer ( Entoderm ) the lungs, liver, intestines, and pancreas develop. It's almost unimaginable that the embryo is only about one millimeter in size!

Questions for your doctor

I have light bleeding – could this be my period?

Even now, it can still be implantation bleeding ( Nidationsblutung ). You might notice light, bright red or brownish bleeding. This occurs when fine blood vessels are injured during implantation—implantation bleeding is therefore no reason to worry. When women are unaware of their pregnancy, it is often mistaken for a period. If you are unsure or experiencing pain, it is best to contact your doctor. You can learn more about this topic in the article „ Bleeding during pregnancy ".

I have drunk alcohol or smoked. Did that harm my baby?

Many women ask themselves this question, especially those who did not expect to be pregnant. In the first weeks of pregnancy, the so-called "all-or-nothing principle" applies. This means that if the embryo is damaged by external influences, it either develops normally or is lost, resulting in an early miscarriage. Only once the organs begin to develop can the embryo’s development be negatively affected by the consumption of alcohol, nicotine, drugs, or other harmful substances—especially during the critical phase between the 5th and 12th weeks of pregnancy. At the latest, once you find out about your pregnancy, you should immediately abstain from alcohol and cigarettes.

Can I safely determine if I am pregnant?

Maybe you are already noticing some early signs of pregnancy or have a suspicion. However, pregnancy can be reliably confirmed by a blood test at the earliest at the end of the 4th week, or by a urine test from the 5th week of pregnancy. Therefore, a negative pregnancy test does not necessarily mean that you
are not pregnant—under certain circumstances, the amount of hCG in your body is simply still too low. Just try again in a few days. Conversely, a positive pregnancy test almost certainly means that you are expecting a baby!

Early miscarriage

Your child is still a tiny cluster of cells and very delicate. During this phase of pregnancy, early miscarriages—often unnoticed—frequently occur. The embryo now reacts especially sensitively to external influences such as alcohol, nicotine, or medications, and about half of all pregnancies end before the fourth or fifth week. Nevertheless, it is important to know that a miscarriage is not always due to the mother's misconduct. Genetic changes in the embryo that prevent its development, infections, hormonal imbalances, or other causes can also lead to an early miscarriage. In the video "Early Miscarriage," midwife Sissi discusses this sensitive topic and how to handle it.

This is now important

• Alcohol and cigarettes are now off-limits. If you are taking medication, consult your doctor to see whether it is still safe to take
  it or if there are alternatives.

• Even if you are already suffering from morning sickness and don't have much of an appetite, continue to pay attention to a balanced diet and consume enough folic acid .

• One of the first signs of pregnancy that many women feel now is fatigue. Take regular breaks and avoid stress as much as possible. Although your pregnancy is not yet visible, your body is currently performing at its best.

• Pay close attention to kitchen hygiene during this sensitive phase. Some raw foods such as fish, raw milk products, and eggs, as well as sprouts and pre-packaged salads, are often contaminated with so-called Listeria , which can cause listeriosis. The risk of illness is many times higher for pregnant women. The infectious disease can be transmitted to the unborn child and, in the worst case, lead to a miscarriage. Therefore, make sure to heat foods to at least 70 degrees, wash fruits and vegetables thoroughly, and avoid raw milk products, raw fish, and raw meat. In the article “ Proper Nutrition During Pregnancy “Find a practical list to download, which lists all the foods that now require caution.”

• An infection with toxoplasmosis can also be extremely dangerous for your unborn child. The infectious disease is often transmitted via cats and their feces.
  If you are not immune to toxoplasmosis (your doctor can determine this through a blood test), it is better for your partner to clean the litter box in the coming months.

With our pregnancy calendar, we want to accompany you through this exciting time and provide you with relevant information, created in exchange with our
LILLYDOO experts. Nevertheless, the information listed here can
never replace personal consultation with your doctor or midwife. Always contact your healthcare professional with questions and for professional care.