If you’re pregnant, you’ve probably heard all about the signs to watch for to determine if you have high blood pressure. High blood pressure, or hypertension, is common during pregnancy. While it isn’t always dangerous, pregnancy-induced high blood pressure is one of the leading causes of pregnancy-related deaths in the U.S., along with embolism and hemorrhage. Hypertension also can increase pregnancy complications, including preeclampsia, placental abruption, gestational diabetes, preterm births, and infant death.
But what about low blood pressure? Should pregnant woman be just as worried about maternal hypotension, or take as many precautions?
Maternal Hypotension Causes
Low blood pressure isn’t always an issue for people. You have low blood pressure when a blood pressure reading is 90/60 or lower. Some people don’t notice anything wrong if they have low blood pressure, but they may experience symptoms when standing up too quickly. Low blood pressure is serious when it causes dizziness, fainting, or shock due to the brain not receiving an adequate supply of blood. Shock requires immediate medical treatment, but you should consult with your doctor if you experience any other symptoms related to low blood pressure.
While pregnancy itself can cause low blood pressure because our circulatory system quickly expands as baby develops, other conditions may be responsible for hypotension. They include:
- Heart problems, such as extremely low heart rate (bradycardia) and heart valve problems, heart attack, or heart failure;
- Endocrine problems, such as thyroid conditions, hypoglycemia, and diabetes;
- Dehydration, such as from vomiting and fever;
- Blood loss, severe infections, or severe allergic reactions;
- Poor pregnancy diet, including not getting enough vitamin B12 or folate, which help produce more red blood cells that regulate blood pressure.
Changes to your blood pressure during pregnancy typically diminish as you return to pre-pregnancy levels after giving birth.
Maternal Hypotension Effects on Fetus
Although the link between hypertension and poor pregnancy outcomes is more established, various issues can occur in pregnant women with hypotension, including an increased risk of stillbirth and fetal growth restriction (FGR).
In one study of 70 pregnant women with hypotension, the babies born to the 30 women who weren’t given medication were found to be “significantly smaller than normal, and the rate of dystrophy was considerably high.” Placental perfusion rates improved significantly with medication, and those babies born to the 40 other mothers who were medicated for hypotension did not differ compared to cases of babies born to mothers with normal blood pressure.
The study suggested that a maternal blood pressure of 110/65 and below should be treated.
Prolonged maternal hypotension is harmful to a fetus and generally associated with nausea and vomiting for the mother. Even a brief episode of hypotension, such as during labor, may results in lower Apgar scores and fetal acidosis.
Maternal Hypotension During Labor
There are several studies relating to hypotension during labor and its issues, particularly with women who undergo C-sections. Hypotension occurs often when a pregnant woman has spinal anesthesia (SA) — up to 80% of the time. A review of recent research found that types of regional anesthesia used matters, and suggests less use of crystalloid prehydration and ephedrine and more use of crystalloid coloading and phenylephrine.
Maternal position also may be important in determining whether a pregnant women will experience hypotension during spinal anesthesia. In a study of 99 women who were full-term and scheduled for elective C-section, what position the women were placed in as well as how the needle was oriented had an effect on hypotension rates. Hypotension was less frequent and the dose of ephedrine lower in women who were positioned left lateral versus tilted supine, but the height of their sensory block and prophylactic measures used also affected the severity of hypotension.
Although the primary outcome in that study was the reduction in the ephedrine requirement, secondary outcomes that were analyzed included maternal blood pressure, highest level of sensory block, fetal Apgar scores, umbilical arterial pH, and base excess values. There were no significant differences in systolic blood pressure or Apgar scores, but the ephedrine requirements varied. The group with the lowest hypotension rates — placed in the full left-lateral position until the start of surgery — had higher umbilical arterial pH values and lower base excess values.
Maternal Hypotension Intervention
Maternal hypotension during labor can be avoided with some common methods, such as leg wrapping, thromboembolic stockings, and preventing aortocaval compression, but vasopressor therapy and intravascular fluid loading are the main prevention methods. Phenylephrine in generally the preferred vasopressor.
Per the maternal position study, no one factor may effectively reduce hypotension in women in labor:
“At present, the management of hypotension during SA in obstetrics remains controversial. Although fluid preload, pushing the uterus to the left side, and use of vasopressor, may often be employed in an attempt to prevent this complication, the incidence of SA-induced hypotension may not effectively decrease with these measures alone. Our approach of directing the bevel of the Whitacre needle laterally and maintaining the patient in the full left lateral position until the start of surgery provided satisfactory blockade for surgery and good hemodynamic stability.”
Some monitoring devices and pre-operative tests may detect hypotension early, which can help in determining the appropriate treatment for mother and baby.
Getting Help with Maternal Hypotension
As always, you should speak with your OB/GYN about any concerns you have during pregnancy, including whether or not your blood pressure levels should be monitored more closely. While hypotension may not be preventable, if you do have a C-section and something happens to you or your baby during surgery because of a mistake a doctor made, you have legal options. Contact Safe Birth Project to see how we can help.