Progesterone is a hormone vital in ovulation and maintenance of pregnancy. Belonging to steroid class, progestogen is mainly produced by the ovary during the initial phases of the pregnancy. When the placenta has developed into a substantial size, it takes over the main production of progesterone. Their level goes up for nine months and then begins to fall, which triggers the onset of labor and delivery. 

What Are the Functions of Progesterone During Pregnancy?

Many do not really understand the relation between progesterone, pregnancy, and unborn babies. By learning the functions of progesterone in pregnancy, you will get the answers.

1. Prepare for Conception

Once an egg has ovulated, the tissue (called corpus luteum) holding it begins to produce progesterone. It thickens lining of uterus and makes it suitable for implantation. Conception occurs when an embryo has implanted itself there. Ovary continues to produce progesterone which works to sustain the initial weeks of pregnancy. If implantation does not occur, estrogen and progesterone levels drop, the endometrium breaks down and menstruation occurs.

2. Support Pregnancy

• As the growth of placenta, its production of progesterone increases, and around 8 weeks, it overtakes that produced by ovaries. Hitherto, pregnancy is preserved by placental progesterone, which also works to relax uterus musculature, stretch it to accommodate a growing fetus and stop premature contractions.
• Progesterone plays a role in physiological changes of mother's immune system, preventing it from attacking the fetus.
• Increase in arterial blood and glycogen in the uterine lining ensures nutrients for the baby.
• Thickening of cervix and creation of a mucous plug prevents bacteria from entering the uterus.

3. Prevent Preterm Labor

In 2011, FDA approved the use of injecting progesterone starting from 16-20 weeks to prevent preterm labor in women who have had one preterm labor previously. However, it is not suitable for women who are carrying more than one baby or are at risk of a preterm labor but never delivered before.

Normal Progesterone Levels During Pregnancy

Given that progesterone is of crucial importance in maintaining a pregnancy, pregnant women should have certain levels of progesterone throughout their term in order to have a normal baby. Let's focus on what these levels are:

1. One to Two Weeks: 1-1.5ng/ml is the amount produced by the ovaries in the first 2 weeks of pregnancy. Pregnancy is counted from the first day of last period.

2. Three to Four Weeks: Level of progesterone produced by the ovary followed by ovulation is around 2ng/ml. Fertilization occurs during 3rd week, increasing the amount of progesterone by 1- 3ng/ml daily. Maximum levels: 10-29ng/ml.

3. Five to Six Weeks: The normal levels are 10-29ng/ml, minimum expected range being 6-10ng/ml. For the progesterone, pregnancy uses it to supply nutritional support to the embryo by increasing the blood supply to the placenta.

4. Seven to Fourteen: By this time the placenta has taken over the production of progesterone. The levels first plateau and then rise towards the end of the first trimester. The range is 15-60g/ml, higher if it's a multiple pregnancy. 

Progesterone Levels throughout your menstrual cycle and pregnancy

1. Progesterone during menstrual cycle:

Day 1-14 --- 1 to 1.5ng/ml

Day 15-28 --- 2-28 ng/ml

2. Progesterone during pregnancy

First Trimester --- 9-47 ng/ml

Second Trimester --- 17-147 ng/ml

Third Trimester --- 55-200 ng/ml

Why Does Low Progesterone Happen?

Spotting or sparse bleeding may indicate low progesterone levels which increase the chance of having a miscarriage. If progesterone levels are low, loss of pregnancy symptoms and excruciating cramps are also seen. Here are some reasons behind low progesterone levels during pregnancy:

1. Ectopic Pregnancy

Although rare, one of the causes of low progesterone levels in early pregnancy can be an ectopic pregnancy. This condition occurs due to the misplacement of the blastocyst inside the fallopian tube rather than the uterine wall.

Risk factor of ectopic pregnancy is a constricted fallopian tube, pelvic inflammatory diseases, scar tissues, endometriosis, vaginal bleeding, pelvic, abdominal and lower back pain and dizziness from blood loss.

Ectopic pregnancy is dangerous for the patient and needs immediate medicinal (methotrexate injection) or surgical intervention.

2. Other causes

• Immense levels of estrogen.
• Inactivity
• Insulin resistance
• Unbalanced diet/starvation
• Stress, leading to high levels of cortisol (a stress hormone).

How to Deal With Low Progesterone Levels

Only if you can maintain normal levels of progesterone, pregnancy can be secured and the uterine lining remains intact with no risk of pregnancy loss. Regular doctor visits as well as opting for a healthy, balanced diet is necessary. On some occasions, progesterone supplements need to be taken before or after pregnancy:

• Before pregnancy: Substituting for the progesterone produced by the ovaries before conception, this progesterone helps thicken and prepare the uterus lining for implantation.
• After pregnancy: For sustaining the endometrium until the placenta can develop enough to start producing its own progesterone.

Progesterone supplements can be taken in the following forms:

1. Vaginal products

• Vaginal gel: one daily. The only FDA-approved progesterone to replace frozen embryo transfers and donor egg recipients.
• Vaginal suppositories: wax-based. 2-3 times daily. FDA doesn't approve it but it is widely used.
• Vaginal inserts: for women under 35. 2-3 times daily. FDA approves to use it as progesterone supplement, but not as progesterone replacement.

2. Progesterone oral capsules, which can also be used vaginally, though not formulated nor with FDA approval. Used 3 times daily.

3. Injections: oil-based. Generally used. It is injected into buttocks once a day. This is a most established, old and widely used methods of delivering progesterone.

Precautions of Taking Progesterone

If you are searching words like "progesterone pregnancy" on the internet, you definitely should know the precautions of taking it during pregnancy. High levels of progesterone in the body can cause various complications during a pregnancy. These include:

• Constipation: Along with uterine muscles, progesterone tends to relax smooth muscles of the intestines too, slowing down bowel movements and leading to constipation.
• Headaches: Similarly, headaches are caused by the vasodilation of vessels supplying the brain.
• Moodiness/depression: due to hormonal imbalances.
• Congested nose: relaxation of nostril musculature.
• Tiredness: Increasedprogesterone during pregnancy depresses the CNS or central nervous system, causing unusual tiredness.
• Breast tenderness