Maternal plant-based diet during gestation and pregnancy outcomes

Abstract

Purpose

We aimed to explore the association of vegetarian–vegan diets and pregnancy outcomes.

Methods

A retrospective, web-based study conducted in 2017. Women who delivered < 4 years prior to enrolment where eligible to participate. Participants were allocated to 3 groups based on their self-reported diet during pregnancy: omnivores, vegetarians or vegans. Outcomes of interest including birthweight centile, small for gestational age (SGA), large for gestational age (LGA), preterm birth (PTB), maternal excessive weight gain (EWG) and gestational diabetes (GDM) were compared between the groups.

Results

Overall, 1419 women of which 234 vegans (16.5%), 133 vegetarian (9.4%) and 1052 omnivores (74.1%) were included in final analysis. Maternal vegan diet during pregnancy was associated with a lower birth weight centile as compared to omnivores (42.6 ± 25.9 vs. 52.5 ± 27.0 P < 0.001), a greater adjusted odds ratio (aOR) for SGA (aOR = 1.74; 95% CI 1.05, 2.86) but not with the risk of LGA (aOR = 0.55; 95% CI 0.30, 1.00). Further adjustment for BMI showed similar but nonsignificant associations for SGA and LGA as compared to the omnivore group. Vegan diet was associated with lower risk for maternal EWG (aOR = 0.61; 95% CI 0.44, 0.86) and modest nonsignificant association with GDM (aOR = 0.54 95% CI 0.28, 1.03) which was further attenuated by adjustment for pre-pregnancy BMI. Maternal diet group was not associated with the risk of PTB or low birth weight.

Conclusions

Maternal vegan diet is a protective factor from EWG but associated with a higher risk for SGA and lower birth weight centile. The association between vegan diet and fetal growth was mediated by maternal BMI.

Appendices

Appendix 1: The complete study questionnaire translated

Question	Choices or field type	Additional field
E-mail address	Email
The final 5 digits of Israeli ID card	Number
Did you exclusively breastfeed your baby for at least 4 months? (no other food/baby formula except breastfeeding)
(If the diet has changed during the pregnancy please refer to the last trimester)	Yes/no/my baby is less than 4 months
How would you define your diet?	Omnivore (I consume eggs, dairy, meat); semi-vegetarian (I consume eggs and milk and a little meat or fish); vegetarian (I do not consume meat and fish but consume eggs and milk); vegan (I do not consume eggs, milk, fish or meat); raw-vegan/801010/raw till 4 (mainly/exclusively consume raw food); other
If you chose “other”, please specify
If your diet has changed during the pregnancy please specify (for example, at the beginning of the pregnancy vegetarian and at the end semi-vegetarian). Please specify by pregnancy months
If you are currently vegetarian or vegan, how long before the pregnancy did you start the current diet?	Less than a year; 1–3 years; more than 3 years
How frequently do you consume meat or chicken?	Every day or more often; 2–6 times per week; once a week; 2–3 times per month; once per month or less; totally avoid
How frequently do you consume fish?	Every day or more often; 2–6 times per week; once a week; 2–3 times per month; once per month or less; totally avoid
How frequently do you consume dairy or dairy products?	Every day or more often; 2–6 times per week; once a week; 2–3 times per month; once per month or less; totally avoid
How frequently do you consume eggs or foods that contain eggs?	Every day or more often; 2–6 times per week; once a week; 2–3 times per month; once per month or less; totally avoid
Have you ever smoked?	I’ve never smoked; I did not smoke in the month prior to the pregnancy; I’ve smoked before the pregnancy but not during the pregnancy; I’ve smoked during the pregnancy	If you have smoked, how many cigarettes did you smoke per week?
Did you take a prenatal supplement? (a multi vitamin supplement for pregnancy)	I did not take one at all; once per month or less; once every 2–3 weeks; once a week; once every 4–6 days; once every 1–2 days; once a day or more	Quantity in milligrams (if you remember)
Did you take a B12 supplement? (In addition to the amount in the prenatal supplement)	I did not take one at all; once per month or less; once every 2–3 weeks; once a week; once every 4–6 days; once every 1–2 days; once a day or more	Quantity in milligrams (if you remember)
Did you take an iron supplement? (In addition to the amount in the prenatal supplement)	I did not take one at all; once per month or less; once every 2–3 weeks; once a week; once every 4–6 days; once every 1–2 days; once a day or more	Quantity in milligrams (if you remember)
Did you take a folic acid supplement? (In addition to the amount in the prenatal supplement)	I did not take any at all; once per month or less; once every 2–3 weeks; once a week; once every 4–6 days; once every 1–2 days; once a day or more	Quantity in milligrams (if you remember)
Other supplements? (Please specify dose and the frequency of use)	Text
Did the baby, during the first 4 month of his/her life
Get a vitamin D supplement?	Not at all; once per month or less; once every 2–3 weeks; once a week; once every 4–6 days; once every 1–2 days; once a day or more
Get a B12 supplement?	Not at all; once per month or less; once every 2–3 weeks; once a week; once every 4–6 days; once every 1–2 days; once a day or more
Get other supplements? (please specify)	Text
Was it a multiple birth? (twins, triplets)	Yes; no
Baby’s sex	Male; female
Birth date of the baby	Date
What was your weight prior to the pregnancy?	Text
How much weight did you gain during the pregnancy?	Text
At what birth week + day did the labor take place?
(If you are not familiar with the day please fill in only the birth week)	Text
What was the birth weight?	Text
What was the birth height?	Text
What was the labor type?	Natural birth (vaginal); Caesarean section; assisted delivery (forceps/vacuum); home birth; other
Questions regarding the baby’s growth
I’d appreciate it if you would upload the baby’s growth chart or the vaccination certificate from the child health clinic (‘tipat halav’)	file upload
If uploading the file is not possible; would you please fill in the baby’s weight and height measurements during the 4 months after birth? (From the child health clinic (‘tipat halav’)
Weight and length at 1 month
Measurement date	Date
Weight	Text
Length	Text
Weight and length at 2 months
Measurement date	Date
Weight	Text
Length	Text
Weight and length at 4 months
Measurement date	Date
Weight	Text
Length	Text
Was the baby seriously sick during the first 4 months of her/his life? (For example, a condition that required hospitalization.)	Yes; no	Please specify
What are your current weight and height?
Height	Text
Weight	Text
What are the baby’s father’s current weight and height? (If known)
Height	Text
Weight	Text
What was your birth weight? (If known)	Text
Were you defined as a premature baby?	I was not defined; I was defined as premature baby
Was the father defined as a premature baby?	No; yes
What was the mode of conception?	Spontaneous; hormonal treatments; IVF
Did you suffer from any medical condition at the beginning of the pregnancy? (For example: Crohn’s, cardiac failure, lupus etc.)	Yes; no	If yes—please specify
Did you take medications during the pregnancy?	Yes; no	If yes—please specify
Did you suffer from gestational diabetes?	Yes; no	If yes—please specify
Did you suffer from eclampsia during the pregnancy?	Yes; no	If yes—please specify
Did you suffer from pre-eclampsia during the pregnancy?	Yes; no	If yes—please specify
Did you suffer from anemia during the pregnancy?	Yes; no	If yes—please specify
Did you have any other medical condition during the pregnancy?	Yes; no	If yes—please specify
Did you have complications in previous labors?	Yes; no	If yes—please specify
Were there any birth defects in the current labor? (Omphalocele, cleft palate, other)	Yes; no	If yes—please specify
Did the baby have jaundice that required phototherapy (light) treatment?	Yes; no	If yes—please specify
What’s your birth year?	Birth dates years
How many labors have you gone through before?	Number
Phone – for future contact (optional)	Number
Do you agree that we may contact you in the future via email or phone for detail verification and follow up? (Of course, by agreeing you will not be obligated to anything)	Yes; no
If you are vegetarian or vegan, what is the main reason for choosing this diet?	Health; moral; environmental; other
Where do you live?	Text
Marital status	Married or living with a partner; divorced or separated; widow; single
Education	Elementary; high school; academic; associate degree
Are you a:	Jew; Arabic-Muslim; Arabic-Christian; Christian non-Arabic; Bedouin; Druze; other
What’s your attitude toward religion?	Secular; traditional; religious; ultra-orthodox; atheist; other
What’s your average household net income?	Less than 2000; 2001–4000; 4001–6000; 6001–9000; 9001–12,000; 12,001–15,000; 15,001–18,000; 1800; 1–21,000; 21,001–2; 4000; over 24,000

Appendix 2: Protocol of filtering and processing the crude data

Prior to answering the questionnaire, the participants were asked to fill in an identification number, derived from their Israeli ID number, for future reference (the questionnaire is completely anonymous except for the e-mail data of the participants who had specifically chosen to be contacted).

The identification number consists of 5 digits (out of 8 in the Israeli ID number) so the probability that two participants would have the same number is very low. On the other hand, it’s nearly impossible to retrieve the participants’ ID numbers from this number.

The data from the answered questionnaires was saved in a designated file and was stored on a virtual encrypted disk.

KA separated all the identifying details from the data (e-mail addresses of the participants who had volunteered to give them) and saved them in a separate file. After this point no one, including the researchers, had a way to attribute a questionnaire to a specific participant, save the cases in which clarifications were needed, by which KA extracted the specific mail address from the designated file and contacted the participant.

The data was exported to an EXCEL file and was searched by YK and KA for false information, either sent by accident or intentionally, before exporting the data to an SPSS file for statistical analysis.

While planning the questionnaire, an analysis of the possible errors was made:

• 1. False questionnaire—sent intentionally or by accident. Due to the anonymity of the online questionnaire it’s impossible to ascertain who had answered it and for what purpose. Furthermore, the questionnaire was published for a few months in different web groups and it’s possible that participants had made an honest mistake by answering it more than once on different occasions. When we identified a false questionnaire, we disqualified it.

• Participant numbers—because the number is unique to each person (as explained above), we could identify questionnaires that had been sent by mistake from the same participant. In this case, if no contradiction between the questionnaires was noted, the data was united. In cases of contradiction between the questionnaires, the questionnaires were disqualified except the cases in which the woman had agreed to be contacted and had left an email address. In these cases, a clarification email was sent.

• Repetitive questions—the questionnaire was designed with redundancy, meaning that some questions should have the same or similar answers. This design helps with identifying inconsistencies and exposing false questionnaires. Questionnaires that contained vast inconsistencies were disqualified as having been sent by mistake (for example, a participant who defined herself as a vegan but reported eating meat products every day). The questions from which a consistency could be assessed were questions regarding diet, maternal and new-born birth dates, ages etc.

• 2. False specific data—typing mistakes, misunderstanding of a question or misinterpretation. (For example, participants who defined themselves as vegans while actually being vegetarians according to the standard definition.) In cases, where an error in a specific datum was found, the whole questionnaire was searched for additional errors and if not found then the specific field was erased but the rest of the questionnaire was used. A clarification mail was sent on some occasions (in cases where the participant had agreed to this beforehand).

• Unreasonable data—maternal weight, height, birth weight, birth weight centile, pregnancy weight gain. The data were disqualified if it was on the upper or lower percent, if it wasn’t physiological, and no contact was established with the participant. For example, a participant whose height was under 1 m or over two.

• Unusual birth date—for example, women that reported that they were born after 2010.

• Diet type calculation—because of the loose definition of dietary patterns among the general population, the actual diet type was calculated using the reported frequency and amount of animal-based products, and not by the participant’s self-definition.

• 3. Questionnaires that did not meet the inclusion criteria were disqualified. The criteria were set after consultation with a senior OBGYN and include:

  • Conditions that had existed prior to the pregnancy and that affected the pregnancy—IBD, Type 1 diabetes, hypertension, hypercoagulable states

  • A birth occurring more than 4 years prior to filling the questionnaire—this criterion was arbitrarily chosen to diminish the memory bias.

  • Higher order gestation—twin pregnancies have specific characteristics and were, therefore, excluded.

Errors	Specifics	Cases	Details	Result
False questionnaires	Duplications	62		Questionnaire excluded
	Contradictions	2		Questionnaire excluded
False specific data	Birth week	1		The specific datum was excluded from analysis
	Maternal age	7	maternal year birth or baby’s birth date is missing	The specific datum was excluded from analysis
	Birth weight centile	1		The specific datum was excluded from analysis
	Unavailable BMI	83	Maternal weight or height is missing or unreasonable	The specific datum was excluded from analysis
	Unavailable weight gain category	88	BMI or weight gain data is missing	The specific datum was excluded from analysis
	GDM	2	The GDM data is missing	The specific datum was excluded from analysis
	Maternal weight birth	1		Corrected after contacting participant
	Weight gain during pregnancy—typing mistakes	24		Corrected
	Unreasonable height	15		Corrected after contacting participant
	Unreasonable birth year	12	After 2010	Corrected after contacting participant
Inclusion criteria	Twins’ pregnancies	35		Questionnaire excluded
Inclusion criteria	Birth date > 4 years	15		Questionnaire excluded
	Pre-pregnancy conditions	11	As specified in exclusion criteria	Questionnaire excluded