TABLE 3.

Summary of studies of folate exposure and allergic outcomes by pregnancy stage, outcome, and exposure¹

Exposure	Periconceptional or first trimester			Second and third trimesters			Any/throughout pregnancy
	Outcome (timing)	Change in risk	Ref	Outcome (timing)	Change in risk	Ref	Outcome (timing)	Change in risk	Ref
Folic acid–containing supplement use (yes or no)
	LRTIs, Hosp (18 mo)	▲▲	24	18 wk, 32 wk: AT (7–8 y)	▬ ▬	34	LRTIs, Hosp (18 mo)	▬ ▬	24
	AD; Specific IgE; Tot IgE (2 y)	▬ ▬ ▬	232	LRTIs, Hosp (18 mo)	▬ ▬	24	AD, Specific IgE, Tot IgE (2 y)	▬ ▬ ▬	232
	E, FEV, FVC (6–7 y)	▬ ▬ ▬	232	URTIs (1–8 y)	▬ ▬ ▬ ▬ ▬ ▬ ▬ ▬	22	E, FEV, FVC (6–7 y)	▬ ▬ ▬	232
	PC, 10 wk: AD (to 4 y)	▬ ▬	26	LRTIs (1–8 y)	▬ ▬ ▬ ▬ ▬ ▬ ▬ ▬	22	Peanut allergy	▬	303
	PC, 10 wk: SB (to 4 y)	▬ ▬	26
	Peanut allergy	▬	303	Freq. RTI (1–8 y)	▬ ▬ ▬ ▬ ▬ ▬ ▬ ▬	22
				Eczema (1–8 y)	▬ ▬ ▬ ▬ ▬ ▬ ▬ ▬	22
				S, BHR (8 y)	▬ ▬	22
Folic acid intake other than supplement (yes or no)
	E (2 y)	▬	28	Allergy, S, E (1 y)	▬ ▬ ▬	31
				Food rxn, IgE, S (1 y)	▬ ▬ ▬	31
Dietary folate intake
	PF Qr4:Qr1: AD, SB (to 4y)	▲ ▬	26	Allergic rhinitis, E (5 y)	▬ ▬	32	E (16–24 mo)	▬	35
				AT (7–8 y)	▬	34
				RBC Qn5:Qn1: AD, AS, Tot IgE (2 y)	▬ ▬ ▬	232
				RBC: Qn5:Qn1: E, FEV, FVC (6–7 y)	▬ ▬ ▬	232
				CBF T3:T.2: Allergy, S, E (1 y) CBF	▬ ▲ ▬	31
				CBF T1:T.2: Allergy, S, E (1 y)	▬ ▲ ▬	31
				CBF T3:T.2- Food rxn, IgE, S (1 y)	▬ ▬ ▬	31
				CBF T1:T.2: Food rxn, IgE, S (1 y)	▬ ▬ ▬	31

¹Studies that reported multiple associations periconceptional and at 10 wk of gestation) or variations of the same outcomes (eg, asthma and wheeze at 1 y or asthma and wheeze at 5 positive findings. However, if there were findings that group individual outcomes (eg, asthma at 3.5, 5.5, and both 3.5 and 5.5 y), only individual denoted exposure time frames. See Supplemental Table 1 under “Supplemental data” in the online issue for all reported findings. Symbols are defined as follows ▲, significant increased risk; ▬, no association. AD, atopic dermatitis; AS, allergic sensitization; AT, atopy; BHR, bronchial hyper-responsiveness; CBF, cord blood folate; E, eczema; FEV, forced expiratory volume in 1 s; FVC, forced vital capacity; Hosp, hospitalized for lower respiratory infections; LRTI, lower respiratory tract infection; PC, preconception; PF, plasma folate; Qn, quintile; Qr, quartile; RBC, red blood cell folate; Ref, reference; RTI, respiratory tract infection; rxn, reaction; S, sensitization; SB, shortness of breath; T, tertile; Tot, total; URTI, upper respiratory tract infection.

²Nested case-control study.

³Case-control study.