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How does dehydration affect hCG?

Human chorionic gonadotropin (hCG) is a hormone produced during pregnancy that is often used to detect and monitor pregnancy. Dehydration can potentially impact hCG levels in a few different ways:

What is hCG?

hCG is a hormone produced by the placenta shortly after implantation. It helps maintain progesterone production in early pregnancy until the placenta is fully formed. hCG levels rise steadily during the first trimester and peak around 10-12 weeks gestation. After this point, levels gradually decline until birth.

hCG can be detected in blood and urine. Urine hCG tests are commonly used for at-home pregnancy testing. Quantitative hCG blood tests can track the rise and fall of hCG levels during pregnancy. Doctors may order serial quantitative hCG tests to:

  • Confirm pregnancy and monitor progress
  • Assess potential issues like ectopic pregnancy or miscarriage
  • Evaluate molar pregnancies or gestational trophoblastic disease

How could dehydration impact hCG levels?

There are a few ways dehydration may affect hCG measurement:

Concentrated urine

Dehydration leads to more concentrated urine with less fluid volume. Concentrated urine can cause abnormally high results on urine pregnancy tests and urine hCG levels. This does not mean hCG production has increased, only that the same amount of hCG is more concentrated in less urine.

Diluted blood

When dehydrated, the blood also becomes more concentrated. This leads to hemoconcentration, where blood components including red cells, white cells, platelets, and proteins are elevated. Although hCG is not affected, hemoconcentration increases the concentration of other proteins in blood. This makes hCG appear lower than it really is when measured as a ratio to total blood proteins.

Impaired clearance

hCG is broken down by the liver and kidneys and excreted in urine. Dehydration reduces blood flow to the kidneys and may impair renal clearance. Slower hCG breakdown could cause levels to accumulate.

Placental function

The placenta produces hCG, so impaired placental perfusion and function during dehydration could hypothetically affect hCG production. However, there is limited evidence that mild dehydration impacts the placenta enough to significantly alter hCG levels.

How much can dehydration affect hCG levels?

Most research found dehydration can alter hCG levels, but the effects tend to be small:

  • One study found urine hCG doubled with dehydration, while serum hCG decreased slightly.
  • Another study found urine hCG increased by 28% with fluid restriction. Serum hCG was unaffected.
  • Multiple studies found urine hCG rose by 15-30%, while serum hCG did not change significantly.

So while dehydration may cause urine hCG to become more concentrated, blood hCG levels remain relatively stable. Mild to moderate dehydration does not appear to substantially impair placental hCG production.

Tips to get accurate hCG testing

To get the most accurate hCG results:

  • Drink normally and avoid dehydration before testing urine or blood for hCG.
  • Use first morning urine, which is least concentrated, for at-home pregnancy tests.
  • Have blood drawn for quantitative hCG in the morning before becoming dehydrated from daytime activities.
  • Compare serum hCG values, which are less affected, rather than urine hCG if monitoring potential issues.
  • Repeat questionable or unexpected hCG tests 1-2 days later after rehydrating.

How dehydration affects pregnancy

While mild dehydration may not significantly impact hCG levels, chronic dehydration can be harmful in pregnancy. Effects may include:

  • Elevated body temperature – Dehydration impairs thermoregulation. This raises body temperature, which can be dangerous in pregnancy.
  • Reduced blood volume – Lower blood volume decreases perfusion of the placenta and uterus.
  • Contractions – Dehydration can trigger Braxton Hicks contractions.
  • Preterm labor – Severe dehydration is linked with premature onset of labor.
  • Neural tube defects – Dehydration during the periconceptional period may increase risk.
  • Small for gestational age – Chronic dehydration can restrict fetal growth.
  • Thromboembolism – Dehydration thickens blood and raises clotting risk.

Plus, diarrhea or vomiting from dehydration sickness can disrupt nutrition and electrolyte balance.

Guidelines for hydration in pregnancy

To minimize risks of dehydration:

  • Drink 8-12 cups of fluids daily, focusing on water.
  • Increase fluid intake during hot weather or exercise.
  • Drink steadily throughout the day rather than large amounts at once.
  • Choose electrolyte drinks like coconut water for rehydrating with nausea/vomiting.
  • Eat fruits and vegetables with high water content.
  • Monitor urine color – light yellow means well hydrated.

Pregnant women should seek medical care for signs of severe dehydration including dizziness, rapid heart rate, dark urine, or inability to urinate regularly.

The takeaway

Mild to moderate dehydration can cause urine hCG levels to become more concentrated and potentially skew results. However, serum hCG levels remain relatively stable. Chronic dehydration can have more significant effects on pregnancy health and outcomes.

To ensure accurate hCG test results, drink normally and avoid dehydration around the time of testing. Prioritize staying well hydrated during pregnancy to reduce risks to mother and baby.