Maternal Adaptations to Pregnancy

Part 1: Intro and a Case History 

• Practically every organ in the body changes during pregnancy. Test results are altered as well. How do you know if the changes your patient experiences are normal or not?
• It’s important to know about these changes no matter what field you go into, because everyone has the potential to have a pregnant patient (except maybe geriatrics and neonatologists).
  • All specialties see both sexes, even Ob/Gyn. She commonly treats males for STDs to prevent them from reinfecting her female patients.
• Contrary to the belief of some (mostly boyfriends), pregnancy is not pathologic. It’s a normal process.
• And without further ado, here is the case that will be analyzed in this lecture. The italicized portions are the questionable abnormalities.
  • By the end of these notes, you will be able to determine just how abnormal they are!

H.S. was a 16 y.o. G1 P0000 whose last menstrual period was 3/18/02, estimated date of delivery was 12/14/02, she presented for her initial prenatal care visit on 7/20/02. She reported no medical or surgical history. She had no known allergies and took no medications. She did not smoke, did not drink alcohol, or caffeinated beverages. She was in 10^th grade at a local high school. She had no pertinent FMedhx. She presented for care because she had confided in her parents that she was pregnant. On review of symptoms, she reported some fatigue and occasional headaches, esp when she hasn’t eaten. She would occasionally feel short of breath after moderate exercise. She had noticed that her gums bled when she brushed her teeth and she had nasal congestion with no other symptoms of URI and thought she was developing allergies. She had some nausea and vomiting earlier in the pregnancy, but that had gotten better over the preceding weeks, but she was also noticing that she had a “sour stomach” and felt a lot of heartburn. She had been noticing that she was getting a darkening of the skin around her face and a line was visible on her belly, as well as stretch marks. She had also been urinating frequently. Her breasts were sore. She was concerned that all these things were happening to her body and that there was something wrong with the baby because she hadn’t felt it move. On physical exam, she was a WD/WN young woman in NAD. Her vital signs were BP 100/64 HR 80 RR 18 T 98.6. HEENT was normal except she had beefy red turbinates with slight transudate. CV exam was normal except for a grade 1-2 SEM at the left sternal border. Abd gravid with the fundus palpable at midway from symphysis pubis to umbilicus. Speculum exam showed a small amount of whitish discharge in dependent portions of her vagina. Bimanual exam revealed a 16-18 week uterus. Ext and neuron exam were normal. She had a slight hyperpigmentation on the mask of her face as well as a prominent linea nigra and slight pinkish markings on her abdomen. A fetal heart was audible on doptone with a rate of 156 bpm. Lab tests done prior to her visit show her WBC 13 (elevated), Hgb 11, Hct 32 (both low), Plt 220 (slightly low). A Udip shows nitrates and leukocytes. All other labs are normal.

Part 2: Cardiovascular Changes 

Functional Changes

• There is an increased cardiac output.
  • At first, this is caused by a slightly increased stroke volume.
  • Later, the stroke volume returns to normal near the end of the 2^nd trimester and the heart rate increases in compensation.
  • It is not unusual to see cardiac outputs of approximately 7.
• There is an increase in total body water, up to 6-8L.
  • This is predominantly in the extracellular fluid, not in the intravascular spaces.
  • However, blood volume still does increase up to 40%.

• There is an increased oxygen demand when pregnant. Coupled with the increased cardiac output, there is less room for compensation during exercise. This leads to a decreased exercise tolerance.
  • Just think ladies, you might not actually be out of shape from the holidays. You could be pregnant! (No such luck for me…)
• Intravascular pressures are also altered during pregnancy.
  • Systolic blood pressure decreases. They are lowest late in the 2^nd trimester (~28 weeks).
  • Diastolic blood pressures decrease as well, but to a lesser amount.
  • These blood pressure changes are due to progesterone, which causes smooth muscle relaxation.
  • Both systolic and diastolic pressures return to normal near the end of pregnancy and may even overshoot slightly before delivery.

Anatomic Changes

• The heart is displaced upwards and to the left.
  • Combined with a raising of the diaphragm, a pregnant heart on a radiograph appears enlarged.
    • Remember this, future radiologists of the world (Jaymin?)! Don’t harass the ob/gyn’s when you see pregnant hearts. It isn’t cardiomegaly.
• Because of the increased blood volume, it is not uncommon to develop a systolic ejection murmur, heard most clearly on the left sternal border.
  • This is not abnormal, but beware of a diastolic murmur. They are never normal and need to be evaluated.
• There can be a pronounced physiologic splitting of S2, particularly upon inspiration.
• Around 28 weeks, when all cardiovascular changes are greatest (blood pressure, heart rate, etc.) an S3 gallop may be heard. This, too, is normal.

Mechanical Effects and Blood Flow Changes

• Supine hypotension syndrome (inferior vena cava syndrome) is due to the increasing size of the uterus.
  • When a pregnant woman lays down, the gravid uterus falls back, pressing on the great vessels.
  • Of the aorta and the IVC, which do you think gets compressed?
    •  That’s right, the IVC! Very good. Its walls are thinner and more easily distensible.
  • This compression leads to a decreased venous return and a decreased cardiac output, leaving the woman dizzy and short of breath while lying down.
    • Ordinarily, if you feel dizzy, you lie down. Counterintuitively, you have to get up in order to feel better here.
• Another general problem that can also be related to IVC syndrome is thrombosis.
  • Venous return is inhibited and blood pools in the dependent regions of the body.
  • This venous stasis can lead to increased risk of thrombosis.
  • It doesn’t matter if you’re standing (generally a stasis issue and worse when pregnant) or lying down (IVC syndrome.
• The Poseiro Effect is due to compression of the aorta.
  • This is typically a problem seen in patients that are full term because the uterus is otherwise not large enough to significantly compress the aorta.
  • The compression is more severe during uterine contractions.
  • When less blood gets through the aorta, less blood gets to the fetus, leading to fetal hypoxemia.
  • To avoid this as much as possible, patients in labor are always put in left lateral uterine displacement.
    • I’ve seen this before and it’s normally done by putting a rolled up sheet or a pillow under the right hip, forcing the uterus and the rest of the very pregnant belly to the left.
• Regional blood flow is increased, particularly to the kidneys, skin, breast, and uterus.
  • The uterus in particular sees a huge increase in blood flow.
    • Normally, the uterus receives 2% of cardiac output.
    • By the time of delivery it is receiving 17% of cardiac output. That’s a huge increase.
    • To put quantities of blood to this, the change is from 100cc/min to 1200cc/min.
    • This is why post-partum hemorrhage is so dangerous. A woman can rapidly exsanguinate.

Continue to Section 2 of Maternal Adaptations to Pregnancy 

Continue to Section 3 of Maternal Adaptations to Pregnancy 

Back to the Reproductive System Index