Pregnancy The Science of Nutrition

Vitamin D In Pregnancy: Why (and How) to Test

Steph Greunke

Vitamin D In Pregnancy: Why (and How) to Test

Table of contents

  • Intro
  • Because You Don’t Know How Much You Need Until You Test
  • Because Many Women Are Deficient
  • Because Vitamin D is Important For Mama and Baby
  • Because Signs of Vitamin D Deficiency Can Be Hard to Identify
  • Don’t Guess, Test

0 min read


Vitamin D has been a hot topic lately. We know it is so important for our health, especially during childbearing years, but how much do we really need? How much is enough and how much is too much? 

What makes these questions so hard to answer is that the answer is, “it depends.” The amount of Vitamin D you need depends on your current levels, and the only way to know your current levels is to test! Why is testing so important? Read on to find out.

Because You Don’t Know How Much You Need Until You Test

It can be hard to determine just how much Vitamin D you need to take because your optimal dosage depends on so many other factors. Your current levels (many women are already deficient), your genetics, diet, geography, age, life stage (whether you are nursing, between pregnancies, had pregnancies in quick succession) and many other factors determine just how much Vitamin D you need.

Our prenatal provides a supportive dose of 4000 IU. This dose is higher than most every other prenatal vitamin on the market, and has been considered safe and effective in achieving sufficiency in all women and their neonates regardless of race and geography in a double blind, randomized clinical trial. This dose is great for pregnant mamas with Vitamin D levels already within an optimal range, but if you entered into pregnancy already deficient (common in many women, especially those who have babies in close succession), you may actually need more. In addition, if you are breastfeeding, a minimum dose of 6,000 IU is recommended to meet the needs of both mama and baby (assuming mama is already within healthy ranges of 30-50 ng/ml or 75 - 125 nmol/L). (Note: A leading randomized controlled trial recommends 6,400 IU for breastfeeding in order to fully support maternal and infant Vitamin D needs. Many mamas choose to directly supplement infants at 400 IU/day. Our baseline dosage recommendation of 6,000 IU for breastfeeding reflects this.

But the only way to know for sure is to test. Unfortunately, most OBs and midwives do not include Vitamin D in preconception or prenatal lab work. Once you get your test results back, you can adjust your dose accordingly. Always check with your practitioner, but the following general guidelines can help inform your dose.

Because Many Women are Deficient

You might think you eat pretty well and spend a decent amount of time in the sun, so you’re probably within reasonable levels. But the reality is, many women are actually deficient in Vitamin D! Research shows that 69% of American women, 65% of Canadian women, 77% of German women, 91% of Chinese women, 96% of Indian women, and 67% of Iranian women have inadequate Vitamin D levels. The reason for variability in rates include genetics, geography, and other factors. And, these estimates are likely low, as they tend to use standard reference ranges rather than optimal ranges when gathering data. In fact, several of our practitioner partners have reported rates of deficiency in pregnant and lactating women in their practice of over 90%, even in sunny Southern California! 

Vitamin D requirements are elevated in pregnancy and breastfeeding, and even if you’re lucky enough to get sun daily, the amount of UV exposure available for the synthesis of Vitamin D depends on many factors other than just time spent outdoors, including the amount of skin pigmentation you have, your body mass, the degree of latitude at which you live, the season, the amount of cloud cover, the extent of air pollution, the amount of skin exposed, and the extent of UV protection you use (clothing cover and sunscreen). 

Because Vitamin D is Important For Mama and Baby

Vitamin D is not a nutrient to mess around with, especially in preconception, pregnancy, and postpartum. It is necessary for the following:

Because Signs of Vitamin D Deficiency Can Be Hard to Identify

Vitamin D deficiency during pregnancy and breastfeeding impacts both mama and baby. But unfortunately, the signs of deficiency can be hard to identify in mama. Many of the signs and symptoms can easily be written off as a pregnancy or postpartum symptom:

  • Immune deficiencies/getting sick often
  • Fatigue/tiredness
  • Bone pain
  • Muscle pain
  • Poor wound healing
  • Hair loss
  • Depression/irritability

Baby relies on mama for Vitamin D while in the womb and while breastfeeding (or on formula). If mama is deficient, baby can be too. But unfortunately, the signs of Vitamin D deficiency in babies often don’t show up until damage has already been done and sometimes even until they’ve reached toddler or child years. Potential risks of deficiency in babies include:

Don’t Guess, Test

While your Vitamin D levels might be optimal, there’s no way to know without testing. And if they aren’t, testing will help you uncover valuable information to address your deficiency and help set you and baby up for a healthy pregnancy and childhood. 

We recommend testing and retesting your levels before pregnancy, ideally once per trimester, and then again postpartum - between birth and 6 weeks, and every six months afterward, at least as long as you are breastfeeding. Testing and retesting your levels empowers you to better understand your unique Vitamin D needs as a first step in optimizing you and your baby’s well being.

Like the article? Share it!

Steph Greunke, MS, RD, CPT, PMH-C

Stephanie Greunke is a registered dietitian that specializes in prenatal/postnatal nutrition, behavioral psychology, and holds additional certifications in perinatal mental health and fitness. She's a key contributor and advisor to Needed as well as Needed’s Head of Practitioner Relationships. Steph is the owner of Postpartum Reset, an online postpartum nutrition course, and the co-host of "Doctor Mom" podcast.