The concentration of surfactant protein-A in amniotic fluid decreases in spontaneous human parturition at term

Figures & data

Table I.  Demographic and clinical characteristics.

Characteristics	Mid-trimester (n = 29)	p^†	Term no labor (n = 28)	p^‡	Term in labor (n = 26)
Maternal age, years	36 (26–40)	<0.001*	24 (14–42)	0.2	22 (15–36)
Gestational age at amniocentesis, weeks	16 (15–18)	<0.001*	39.3 (38–42)	0.3	40 (38–42)
Gestational age at delivery, weeks	39 (37–42)	0.6	39.3 (38–42)	0.3	40 (38–42)
Birth weight, grams	3460 (2866–4043)	0.3	3330 (2810–4470)	0.2	3325 (2540–3760)
Male gender, n (%)	17 (58.6%)	0.1	11 (39.3%)	0.03*	18 (69.2%)

Values are presented as median (range) or number (%). *p < 0.05. ^†Comparison between mid-trimester and term no labor. ^‡Comparison between term no labor and term in labor.

Figure 1. The median concentrations of SP-A and of SP-B in amniotic fluid were significantly higher at term than in the mid-trimester of pregnancy (SP-A term no labor: median 5.6 μg/mL, range 2.2–15.2 μg/mL vs. mid-trimester: median 1.64 μg/mL, range 0.1–4.7 μg/mL; p < 0.001, and SP-B term no labor: median 0.54 μg/mL, range 0.17–1.99 μg/mL vs. mid-trimester: median, 0 μg/mL, range 0–0.35 μg/mL; p < 0.001). The median amniotic fluid concentration of SP-A in women at term in spontaneous labor was significantly lower than in those not in labor (term in labor: median 2.7 μg/mL, range 1.2–10.1 μg/mL vs. term no labor: median 5.6 μg/mL, range 2.2–15.2 μg/mL; p < 0.001). There was no significant difference in the median amniotic fluid concentration of SP-B between women with and without labor (term in labor: median 0.47 μg/mL, range 0.04–1.32 μg/mL vs. term no labor: median 0.54 μg/mL, range 0.17–1.99 μg/mL; p = 0.2). *p < 0.05.

Figure 2. After adjusting for total protein concentration, the median amniotic fluid concentrations of SP-A and of SP-B were significantly higher at term than during the mid-trimester of pregnancy (SP-A/total protein, term no labor: median 3.05 μg/mg, range 1.15–6.87 μg/mg vs. mid-trimester: median 0.36 μg/mg, range 0.09–1.59 μg/mg; p < 0.001, and SP-B/total protein, term no labor: median 0.30 μg/mg, range 0.03–2.11 μg/mg vs. mid-trimester: median 0 μg/mg, range 0–0.08 μg/mg; p < 0.001). Amniotic fluid SP-A concentration after adjusting for total protein concentration in women at term in labor was lower than that for those not in labor (term labor: median 1.45 μg/mg, range 0.8–25.18 μg/mg vs. term not in labor: median 3.05 μg/mg, range 1.15–6.87 μg/mg; p < 0.001). There was no significant difference in the median amniotic fluid concentration of SP-B/total protein in women with and without labor (term labor: median 0.23 μg/mg, range 0.04–5.58 μg/mg vs. term not in labor: median 0.30 μg/mg, range 0.03–2.11 μg/mg; p = 0.2). One data point in the term labor group was an outlier (SP-B/total protein: 5.58 μg/mg) and is not shown in the figure. *p < 0.05.

Figure 3. Amniotic fluid concentrations of SP-A in women at term with and without labor stratified by gender of the fetus. There was no significant difference in the median amniotic fluid concentration of SP-A stratified by fetal gender in both the term in labor and term not in labor groups (term no labor SP-A, female: median 5.7 μg/mL, range 2.2–15.2 μg/mL vs. male: median 5.3 μg/mL, range 2.6–11.7 μg/mL; p = 0.8, and term in labor SP-A, female: median 2.4 μg/mL, range 1.7–4.1 μg/mL vs. male: median 3.0 μg/mL, range 1.2–10.1 μg/mL; p = 0.2).

Figure 4. Amniotic fluid concentrations of SP-B in women at term with and without labor stratified by gender of the fetus. There was no significant difference in the median amniotic fluid concentration of SP-B stratified by fetal gender in both the term in labor and term not in labor groups (term no labor SP-B, female: median 0.5 μg/mL, range 0.2–1.9 μg/mL vs. male: median 0.5 μg/mL, range 0.2–1.1 μg/mL; p = 0.9, and term in labor SP-B, female: median 0.4 μg/mL, range 0.2–0.9 μg/mL vs. male: median 0.5 μg/mL, range 0.04–1.3 μg/mL; p = 0.8).