WOW! What an excellent question!
There are quite a few things to do:
1) Go 100% Organic in the home. Organic, though not perfect, is much better than GMO, pesticide laden foods. Buy from a health food store or the organic section of a conventional store. I discuss organic in lesson 3 of my book, right here:
https://www.unvaccinatedchildren.com/courses/the-beginners-guide-to-natural-living/
2) Make your entire home nontoxic. This means laundry detergent, cleaning supplies, dish soap, shampoo, soap, etc. You can find all of these items in a health food store. Conventional laundry detergent is toxic and should be immediately replaced. I use BioKleen citrus detergent. I discuss the health food stores and nontoxic products in lesson 4 of my book:
https://www.unvaccinatedchildren.com/courses/the-beginners-guide-to-natural-living/
3) Take vitamin C every day. Vitamin C builds the immune function and also helps to ensure a better / easier birth. Minimum 1 gram per day - 3 grams per day is probably a good amount. Every day starting now and all the way through pregnancy. Dr. Klenner had 300 consecutive uncomplicated births by ensuring his pregnant patients took vitamin C every day. More here:
4) Do a colon cleanse and enema or colonic to remove toxins from the digestive tract. I discuss this type of detoxification in lesson 7 of my book:
https://www.unvaccinatedchildren.com/courses/the-beginners-guide-to-natural-living/
5) Reduce processed foods (even if organic) in the diet, including bread, soda, pasta, cereal, muffins, crackers, etc., and opt for more whole food options, usually found in the produce section. Eating apples, oranges, pears, berries, etc, instead of sweet pastries, is preferred (as an example). I discuss processed foods in lesson 2 of my book:
https://www.unvaccinatedchildren.com/courses/the-beginners-guide-to-natural-living/
6) Do a full heavy metal detox along with the addition of trace minerals every day for six months. This zeolite detox pack would be a perfect one to use:
https://smv.thegoodinside.com/shop/product/zeolite-fulvic-pack-mx
7) Go to my online course about raising vaccine free children and review lesson 7 where I discuss pregnancy and birth topics, vitamin K, and much more, so that you can prepare accordingly:
https://www.unvaccinatedchildren.com/courses/how-to-raise-healthy-vaccine-free-children/
8) Consider a home birth or a birthing center over a hospital birth. Hospitals are NOT relaxing and they do not put the woman into the best position for birth; at a birthing center or home birth the proper position can be used, water for a water birth can be used, and in a more relaxed environment, the birth process is radically easier. Plus, you don't have to worry about the HepB vaccine, eye cream antibiotic or vitamin K shot being pushed onto you. Here is a quick overview about home birth:
https://hearthandhomemidwifery.com/blog/reasons-to-consider-home-birth-over-hospital-birth
9) Learn more about why to avoid all vaccines and what to do when your child is ill by visiting my Vaccine Free QuickStart Guide - review, watch both embedded videos, purchase the first two books:
https://www.unvaccinatedchildren.com/vaccine-free-quickstart-guide-for-parents/
SUMMARY
A healthy pregnancy begins with healthy eating (organic), creating a nontoxic living environment, detoxification (digestive tract AND heavy metal), taking supplements (especially Vitamin C), and learning all about the various nuances of pregnancy and birth.
Hope this helps!
Make sure you know your MTFHR gene status. Mutations on that gene can set one up for pre=eclampsia/eclampsia.... all for a lack of biological active folic acid (flolinic or 5 methyl-folate)