Table 2.

Cord anti-PT IgG levels with different avidities of women vaccinated with Tdap during early and late third trimester.

	Vaccinated during 28–32 WG (n = 43)	Vaccinated during 33–36 WG (n = 47)	P	Adjusted P*
Total anti-PT IgG levels (IU/mL), GMC (95% CI)	75.3 (61.2–92.9)	52.66 (39.9–69.6)	0.046	0.038a
Total RAI of anti-PT IgG (AU), mean (SD)	136.5 (28.4)	143.3 (34.7)	0.313	0.317**
Total absolute avidity levels of anti-PT IgG (AAU/mL), GMC (95% CI)	100.0 (78.3–127.8)	73.1 (53.3–100.3)	0.128	0.119**
Fractional absolute anti-PT IgG levels (IU/mL) with different avidities, GMC (95% CI)
Very low	1.2(0.5–2.6)	0.9 (0.5–1.7)	0.667	0.675b
Low	2.0 (1.1–3.9)	2.0 (1.1–3.6)	0.986	0.759c
Low–medium	11.2 (8.5–14.7)	6.9 (4.7–10.2)	0.051	0.054**
Medium	11.6 (8.8–15.2)	6.7 (5.2–8.6)	0.005	0.007d
Medium–high	11.4 (8.2–15.8)	7.5 (5.2–10.7)	0.088	0.090**
High	10.1 (7.4–13.8)	5.7 (3.6–8.9)	0.042	0.035a
Very high	11.2 (8.1–15.3)	7.7 (4.7–12.5)	0.210	0.268e

PT, pertussis toxin; IgG, immunoglobulin G; Tdap, tetanus-diphtheria and acellular pertussis; WG, weeks gestation; RAI, relative avidity index; IU, international unit; SD, standard deviation; AU, Avidity Unit; AAU/mL, Absolute Avidity Unit/mL.

^*For each specific anti-PT IgG levels, Univariate linear regression analysis was used to identify baseline characteristics variables that could potentially impact the specific anti-PT IgG levels. This was followed by multi-variate regression model, for each anti-PT IgG levels, that adjusted for potential confounders detected in univariate regression analysis as well timing of vaccination in pregnancy. The adjusted P-value is presented.

^**No other variable (other than timing of vaccination) with p ≤ 0.25.

^aAdjusted for gestational age at birth (weeks).

^bAdjusted for ethnicity and delivery mode (Caesarian Section or vaginal delivery).

^cAdjusted for gestational age at birth (weeks), gestation at delivery (≤ 37, >37 weeks).

^dAdjusted for gestation at delivery (≤ 37, >37 weeks).

^eAdjusted for ethnicity.