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The First 1000 Days - Probiotics + Enhancing Baby's Immune System Starting At Conception
The first 1000 days shape baby's microbiome and immunity. Learn how probiotics before and during pregnancy support a healthy start for both mom and baby.
Written and medically reviewed by Dr. Courtney Ranieri, ND, a licensed naturopathic doctor registered with the College of Naturopaths of Ontario (Reg. #3726). Last reviewed July 2026.
The First 1000 Days
A growing body of evidence shows that the first 1000 days of life, starting even before baby is born (from conception to 2 years old), play a major role in developing a healthy microbiome and immune system for the rest of baby's life.
Why is the microbiome so important?
The microbiome (the collection of bacteria found in the gut) is extremely important for overall health. In recent years, the increase in allergic and autoimmune conditions such as obesity, diabetes, IBS/IBD, celiac disease and MS has been attributed, in part, to changes in gut bacteria, including a decrease in the amount and strains of bacteria found in the gut.
What are probiotics?
Probiotics are the living, healthy bacteria that live in the gut and help regulate digestive and immune function. There's almost 4 lbs of bacteria living in an adult human's digestive tract. Probiotics are found in foods (yogurt, kefir, kombucha, sauerkraut and fermented foods) and supplements. Each probiotic has a different variety and number of bacteria per capsule.
Moms who took probiotics before and during pregnancy:
- had a lower risk of pre-term pregnancy
- lower risk of gestational diabetes and preeclampsia
- lower risk of bacterial vaginosis in pregnancy
- babies had a lower risk of atopic conditions like allergies, eczema and asthma
What other factors influence baby's microbiome?
- Birth method (vaginal vs. C-section)
- Feeding method (breastfeeding vs. formula)
- Environmental exposures
- Prenatal diet and probiotic use
- Antibiotic use
How do you choose the right probiotic?
- Work with an ND to pick one with strains specifically researched for your concerns (there are probiotics to help with bloating, indigestion, eczema, vaginal health, UTIs and more).
- Look for a variety of strains. The gut has over 1000 strains, and probiotics tend to work best with more than one.
- Check the CFU count. Probiotics should contain live cultures (colony-forming units). I look for a high CFU (5 billion or more) so the bacteria can create a healthy home in the gut.
Thinking about conceiving? Working with a Naturopathic Doctor on a targeted prenatal plan can help improve both mom and baby's health.
Always check in with your primary health practitioner before starting or making any changes to your healthcare plan.
About the author
Dr. Courtney Ranieri, ND is a board-licensed naturopathic doctor and the founder of Somewhere Health. She earned her Doctor of Naturopathic Medicine at the Canadian College of Naturopathic Medicine in Toronto and holds an Honours Bachelor of Science from the University of Western Ontario. Her clinical focus spans hormonal health, fertility, digestion, and women's health, with advanced training in pelvic floor therapy and integrative fertility care.
