Which general body system undergoes the most profound change during pregnancy?

This chapter reviews the major physiological adaptations during pregnancy and also highlights changes in the reference ranges of common laboratory values encountered in pregnancy. Pregnancy induces a myriad of changes involving the cardiovascular system, respiratory system, gastrointestinal and hepatobiliary systems and genitourinary system. Pregnancy is associated with an overall increase in the serum concentrations of total cortisol, free cortisol, aldosterone, deoxycorticosterone, corticosteroid binding globulin, and adrenocorticotropic hormone. Pituitary enlargement occurs in pregnancy by estrogen mediated proliferation of prolactin-producing cells. During the first trimester of pregnancy, total thyroxine and total tri iodothyronine concentrations begin to increase and peak at mid-gestation, primarily as a result of increased production of thyroid-binding globulin. The immunological adaptations of pregnancy, particularly at the maternal-fetal interface, comprise complex mechanisms that enable the fetus to grow while preventing the mother from rejecting the fetus.

During pregnancy, our bodies undergo some pretty major changes in order to gestate and grow our babies. You likely know you will be flooded with hormones and your skin and muscles and organs must stretch and grow to accommodate your growing baby.

But you might not be prepared for how almost every one of your bodily systems changes and has a role to play when you become pregnant. Some of these changes may be more pronounced than others—and the intensity (and comfort) can vary considerably from one pregnant person to another.

Still, even when the changes aren't the most pleasant (hello, hemorrhoids and constipation!), it can be gratifying to know that your body knows exactly what to do to help guide your baby safely into the world. Here are all the different ways your body and its systems, senses, processes, and more are learning to support your pregnancy.

Your Pregnancy Week by Week

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How Will Pregnancy Change My Body?

Your Endocrine System

The first thing you may notice, before you sense many other physical changes, is what happens to your mood and energy levels. The hormonal rush that happens in early pregnancy can be pretty overwhelming.

You may feel highly emotional, moody—and utterly exhausted. And yes, those pesky hormones are part of what make you sick to your stomach in early pregnancy.

Human chorionic gonadotropin (HCG), human placental lactogen (hPL), estrogen, and progesterone are the main hormones that predominate during pregnancy.

• HCG: A hormone produced by the placenta and helps prepare and support your body for implantation and gestation. It decreases after the first trimester, and may be responsible for making you feel nauseous during your first trimester. 
• hPL: A hormone produced by the placenta. hPL also stimulates the growth of milk gland in your breasts, to prepare you for breastfeeding.
• Estrogen: A hormone produced in Increased amounts in the placenta to help support your pregnancy.
• Progesterone: A hormone that increases substantially during pregnancy and helps with implantation. It contributes to the loosening of your joints so that your body can accommodate your growing uterus and prepare to give birth.

Taste and Smell

It’s not your imagination—your senses of taste and smell change significantly during pregnancy.

You may become a bloodhound, able to smell pleasant (and not so pleasant) smells from a mile away. Foods that once tasted great to you may taste awful—and you may crave foods you’ve never craved before. Some pregnant people also report a “metallic” taste in their mouth during the first trimester.

Blame this all on the changing hormones of pregnancy. Experts surmise that these changes may have a protective effect, as your senses before more fine-tuned and protect you from ingesting anything that may make you sick or endanger your fetus.

Smells Pregnant Women Hate

Weight and Fluid Retention

No doubt, you can expect to gain some weight during pregnancy—anywhere from 25–35 pounds is normal. Usually, the majority of weight gain happens in the second and third trimester.

Most of us don’t have much problem putting on the appropriate amount of weight, as our hunger and need for calories increases. Although you shouldn’t diet during pregnancy, experts recommend you focus on nutritious choices as much as possible.

Some of the weight gain—especially during the third trimester—is from water retention. It’s common to have swelling in your hands, feet, and ankles, especially if you are pregnant during the summer. Like everything else, this discomfort will pass, but it can help to put your feet up, rest, and keep yourself cool and hydrated.

Blood Volume and Circulation

Your blood volume will increase significantly to help support your pregnancy and your baby. This means your need for iron rich food will increase to prevent pregnancy anemia. This increased blood volume also means that your kidneys and urinary system will have to work extra hard to process increased waste.

The increased blood volume also can cause your veins to enlarge in size, increasing your propensity to experience varicose veins as well as hemorrhoids.

Changes in your circulatory system and blood pressure can also make you more susceptible to dizziness and fainting during pregnancy. This may also be due to your expanding uterus putting pressure on your blood vessels as well as appetite and metabolism changes.

Make sure to stay off your feet when needed, eat and drink frequently, stay out of the heat when possible, get up slowly from sitting, and wear loose-fitting clothes. 

Digestion

The hormonal changes you experience can cause nausea, vomiting, food aversions, and food cravings. But hormones aren’t the only things that change how your body handles and processes food during pregnancy. Your digestive system experiences major changes as well.

You may notice constipation, in part to the added weight of your growing uterus on your intestines. The hormones of pregnancy also tend to slow down digestion.

You may also notice an uptick in indigestion and heartburn, especially as you enter the third trimester and your growing baby pushes on your stomach. Eating smaller, more frequent meals can help.

You can talk to your doctor about pregnancy safe antacids and other medication that can relieve some of the more unpleasant digestive symptoms.

Your Breasts, Uterus, and Cervix

One of the most obvious (and sometimes welcome) changes that happen during pregnancy involves your breasts. It’s all in the name of preparing your body to breastfeed your little one.

In the first trimester, your breasts will feel sore and even grow a little. Inside your breasts, milk glands and milk ducts are forming and growing. You may notice more prominent veins as well.

By the end of pregnancy, your breasts will have grown about one cup side. You may notice a whitish/yellowish fluid leaking out of your breasts in mid to late pregnancy. This is called colostrum, and will be your baby’s “first milk.” Make sure to wear a supportive bra as your breasts enlarge.

Your uterus and cervix will also change significantly during pregnancy. Your uterus will increase in size and weight, from the size of your fist in early pregnancy, up to the size of a watermelon by the time you are ready to give birth. Don’t worry—your uterus will shrink back to its original size within a few weeks of giving birth.

During pregnancy, your cervix will thicken and form a mucus plug. By the end of pregnancy, your cervix will soften considerably as it gets ready to thin out and dilate for pregnancy.

You may also notice a thick discharge from your cervix—perhaps tinged with blood—as labor and delivery draw closer. This is often referred to as “losing your mucus plug,” or your “bloody show.”

What Is the Mucus Plug?

Hair and Nails

Be prepared for quite a few changes in the hair and nail department—most of which may make you happy. Due to the hormones of pregnancy, you will likely have a much fuller mane of hair than usual.

You may also notice that your nails grow faster than usual. However, be prepared, because a few weeks into your postpartum period, you may notice that your hair falls out in pretty significant amounts. This is normal, though, as your hair growth is just doing the job of evening itself out.

What Is Lanugo?

Skin

You can also expect some pretty major changes in your skin. First, there’s the “pregnancy glow” that many experience—likely due to hormones and increased blood volume.

You may also notice that your nipples become darker as your breasts undergo changes, or they may look more veiny. You may develop a line from your belly button to your pubic hairline, called the linea nigra. This is normal and will fade after delivery.

There are also some less pleasant changes that happen to your skin. You may notice darker patches of skin on your face called melasma.

You may also experience stretch marks, as your abdomen and breasts grow. Stretch marks during pregnancy are usually found on the belly, breasts, thighs, and buttocks. They start out red, pink, or brown. Within a few months, they will fade to a light pink or silver.

Your skin may also feel extra dry and itchy. This can be normal. However, see your doctor if you experience excessive itchiness in late pregnancy, as it may indicate a serious issue called cholestasis of pregnancy, which can be harmful to your fetus.

How Does Skin Change During Pregnancy?

Your Musculoskeletal System and Joints

Due to loosening joints (caused by the hormone relaxin), weight gain, and your expanding uterus, you are likely to experience quite a few aches and pains in pregnancy. Here are the most common ones:

Back Aches

General back aches and pain are very common in pregnancy. Gentle massage can help with this. Getting regular exercise, but keeping it gentle, can also help. Using a maternity support belt can help distribute your abdominal weight more evenly and ease off your back pain.

Round Ligament Pain

As your belly and uterus expand, you may experience pain in your ligaments, known as round ligament pain. This pain can come on suddenly and feel like pulsating, shooting pain. It is not harmful but can be very uncomfortable. Talk to your doctor about pregnancy-safe painkillers. Using a maternity belt can help, as can heat treatments.

Sciatica

When your uterus and growing baby put pressure on your sciatic nerve, it can cause a lot of discomfort. Sciatic feels like a shooting pain and tingling down one of your hips and legs. The sensation can be felt all the way to your feet!

Usually sciatica resolves after your baby is born, but you can ask your doctor what comfort measures may be helpful to you. Sometimes massage or even a chiropractic adjustment can help.

Leg Cramps

Leg cramps during pregnancy are common, but they can come on suddenly, and surprise you. They are often experienced first thing upon waking or at night. They feel like an intense spasm in your leg muscles.

These cramps are thought to be due to the way your body processes calcium during pregnancy, and relief may come with gentle massage, heat, and increasing calcium in your diet.

Other Changes

If that wasn’t enough, there are several other small changes that you may notice as you progress through pregnancy. For example, you may notice:

• Your vision gets poorer or becomes blurred during pregnancy.
• Numbing or tingling sensations in your hands and feet.
• Your nose is more stuffy, with increased nasal secretions.
• Nosebleeds may be more frequent during pregnancy.
• You have to urinate more during pregnancy and may even leak pee more frequently.
• Your gums may bleed more frequently during pregnancy and your teeth may feel more sensitive.
• You may be more prone to urinary tract infections and yeast infections.
• You may find that you overheat easily.
• You may become dehydrated and famished more easily, as you need more calories and liquids during pregnancy.
• You may be more exhausted during pregnancy, yet you may have more trouble sleeping. Consider investing in a body pillow and sleeping on your left side.

A Word From Verywell 

As completely exhausting and uncomfortable as most of these pregnancy bodily changes are, they are common—and most importantly, they don’t last forever.

However, you should bring up any concerning changes you may be experiencing to your doctor or midwife. Most changes you experience will be minor, normal, and harmless. But sometimes, the changes might indicate a more serious problem or even a medical emergency.

Emergency signs to watch for in pregnancy include:

• Excessive bleeding
• Muscular convulsions
• Sudden changes in vision
• Unusual stomach aches
• Fever/chills
• Extreme headaches
• Excessive vomiting
• Decrease in baby’s movements
• Any thoughts of harming yourself or your baby

Besides these emergency indicators, anytime your gut tells you something is wrong or feels “off,” you shouldn’t hesitate to contact your medical providers. That’s what they are there for.

The good news is that these bodily changes, especially the more uncomfortable ones, are “only for now.” Almost all of them disappear within a few days or weeks of giving birth. And as unsightly, nauseating, painful, and downright maddening some of these changes are, keep in mind that they are all happening in the name of helping to gestate your baby and usher them into the world.

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