TABLE 5.

Risk ratios (and 95% confidence intervals) of each head circumference entity associated with each histologic characteristic

Histologic lesion	Head circumference Z-score
	Vaginal delivery		Cesarean section delivery
	<−2	≥2 to <−1	<−2	≥−2 to <−1
Inflammation chorionic platea	1.0 (0.4–2.8)	1.6 (0.99–2.5)	0.3 (0.1–0.8)	1.0 (0.6–1.7)
Inflammation chorion/deciduab	3.5 (1.3–9.9)	2.4 (1.5–3.9)	0.2 (0.1–0.5)	0.7 (0.5–1.03)
Neutrophil infiltration fetal stem vessels	1.1 (0.4–2.8)	2.4 (1.5–3.7)	0.2 (0.1–0.6)	0.9 (0.6–1.4)
Umbilical cord vasculitisc	2.4 (0.96–5.9)	1.9 (1.2–3.2)	0.3 (0.1–0.9)	1.1 (0.6–1.7)
Thrombosis of fetal stem vessels	0.7 (0.1–5.2)	1.1 (0.5–2.4)	3.0 (1.4–6.4)	1.2 (0.5–2.8)
Infarct	0.6 (0.1–2.8)	1.2 (0.6–2.1)	4.1 (2.6–6.6)	2.7 (1.7–4.0)
Increased syncytial knots	d	1.2 (0.6–2.4)	4.1 (2.6–6.4)	2.1 (1.5–3.2)
Decidual hemorrhage/fibrin deposition	1.1 (0.4–2.8)	0.9 (0.5–1.5)	1.4 (0.8–2.7)	1.5 (0.9–2.4)

Data are presented separately for placentas delivered vaginally (first 2 data columns) and for sample of placentas delivered by cesarean section (last 2 data columns). Only adjustment is for gestational age (23–24, 25–26, and 27 wk).

^aStage 3 and severity 3;

^bGrades 3 and 4;

^cGrades 3, 4, and 5;

^dEmpty cells prohibit calculation of risk ratio.

McElrath. Factors associated with small head circumference at birth among ELGAN. Am J Obstet Gynecol 2010.