Table 1.
Characteristics by Lactation Group, Low Milk Supply Cohort Restricted to Those Who Completed the Follow-Up Test-Weigh Measurements
| External control group, n = 12 |
Low milk supply cohort |
ap | ||
|---|---|---|---|---|
| Moderate/normal milk output nested controls (≥300 mL), n = 12 |
Severely low milk output cases (<300 mL), n = 18 |
|||
| Mean (SD) or Median [Q1–Q3] or % | ||||
| Maternal and infant characteristics | ||||
| Maternal age, years | 32 (4) | 34 (4) | 33 (6) | 0.66 |
| College graduate | 92% | 100% | 67% | 0.05 |
| Primiparous | 33% | 50% | 56% | 0.54 |
| Vaginal delivery | 83% | 75% | 50% | 0.18 |
| Female infant | 67% | 50% | 50% | 0.73 |
| Newborn weight loss ≥10% | 0% | 75% | 83% | 0.0001 |
| Lactation variables | ||||
| Milk output at baseline, g/24 hours | 758 (71) ab |
539 (166) b |
162 (73) c |
<0.0001 |
| Breast emptying events at baseline | 14 (4) a |
25 (8) b |
19 (6) ab |
0.001 |
| Postpartum day started baseline test-weigh | 46 (13) a |
31 (14) b |
28 (17) b |
0.003 |
| Milk output increased, % | n/a | 58% | 50% | 0.72 |
| Maximum milk output, g/24 hours | 758 (71)c a |
604 (151) b |
183 (72) c |
<0.0001 |
| Breast emptying events at maximum output | 14 (4)c | 20 (8) | 17 (4) | 0.06 |
| Postpartum day of maximum output | 46 (13)c | 53 (22) |
40 (18) | 0.18 |
| Postpartum day of final test-weigh | 46 (13)c | 65 (18) | 55 (20) | 0.20 |
| Max milk output ≥600 g/24 hours, % | 100% | 58% | 0% | <0.0001 |
| Metabolic health variables | ||||
| Postpartum day of baseline lab measurements | 51 (13) a |
35 (14) b |
30 (17) b |
0.003 |
| BMI, kg/m2 | 26.2 (6.6) a |
28.4 (4.2) a |
38.7 (8.3) b |
<0.0001 |
| BMI category | ||||
| Normal | 58% | 25% | 6% | 0.003 |
| Overweight | 25% | 42% | 11% | |
| Obese | ||||
| I (30.0–34.9) | 0% | 25% | 17% | |
| II (35.0–39.9) | 8% | 8% | 28% | |
| III (≥40.0) | 8% | 0% | 39% | |
| dWaist circumference, cm | 88.9 (12.3) a |
93.3 (10.1) a |
112.0 (15.5) b |
<0.0001 |
| dFasting plasma glucose, mg/dL | 85 (6) a |
85 (5) a |
92 (8) b |
0.007 |
| Fasting insulin, U/mL | 4.6 [3.8–8.5] a |
6.8 [4.3–8.1] ab |
9.0 [5.9–17.1] b |
0.004 |
| Fasting c-peptide, ng/mL | 1.38 [1.10–2.09] a |
1.63 [1.22–1.84] a |
2.36 [1.96–2.95] b |
0.0007 |
| HOMA-IRC-peptide | 0.29 [0.22–0.47] a |
0.34 [0.24–0.41] a |
0.50 [0.43–0.74] b |
0.0006 |
| dPlasma triglyceride, mg/dL | 63 (29) a |
68 (15) a |
124 (60) b |
0.0005 |
| dHDL cholesterol, mg/dL | 70 (15) a |
61 (10) ab |
55 (13) b |
0.01 |
| LDL cholesterol, mg/dL | 98 (28) | 110 (33) | 120 (39) | 0.24 |
| Total cholesterol, mg/dL | 181 (34) | 184 (33) | 199 (44) | 0.38 |
| dSystolic blood pressure, mm | 103 (10) a |
105 (10) a |
117 (10) b |
0.0008 |
| Diastolic blood pressure, mm | 67 (7) a |
69 (9) a |
80 (9) b |
0.0001 |
| Metabolic syndrome risk z-score | −0.99 (0.67) a |
−0.68 (0.43) a |
+0.39 (0.73) b |
<0.0001 |
| Serum prolactin, basal, uIU/mL | 1,193 [757–1,655] n = 12 |
2,028 [1,524–2,734] n = 6 |
677 [463–2,007] n = 12 |
0.07 |
| Serum prolactin post breastfeeding, uIU/mL | 4,071 [2,267–7,989] n = 12 |
3,199 [2,504–8,539] n = 6 |
3,351 [1,972–7,324] n = 6 |
0.92 |
| Gestational diabetes mellitus | 8% | 0% | 39% | 0.02 |
| Polycystic ovary syndrome | 17% | 8% | 22% | 0.87 |
Notes: milk output, g/24 hours, is based on exclusively breastfed infant intake for external control group and on total milk output for the low milk supply cohort. Breast emptying events/24 hours is the sum of left breastfeeds + left breast expression sessions + right breastfeeds + right breast expression sessions, normalized to 24 hours. For the low milk supply cohort, prolactin was categorized as “basal” if the single blood draw was obtained at least 1.5 hours after the most recent breast emptying episode and categorized as “response” if obtained <90 minutes from the start of the most recent breast emptying episode. For the external control group, “basal” was obtained at least 2 hours after a breast emptying episode and “response” was obtained 30 minutes after the start of the most recent breast emptying episode. To convert prolactin values to ng/mL, divide by 21.2.
p-Value based on ANOVA for continuous variables or log-transformed continuous hormone variables, and Fisher's exact test for categorical variables.
Differing online letters denote significantly different means (p < 0.05) based on ANOVA post hoc Tukey–Kramer test.
Baseline values repeated to enable statistical comparison with follow-up time points in the low milk supply cohort.
This variable is a component of the metabolic syndrome risk z-score, which is an algorithm where 0, >0, and <0 z-scores signify average, worse than average, and better than average metabolic health profiles, respectively, as compared with all U.S. adults aged 20–65 years.
ANOVA, analysis of variance; BMI, body mass index; HDL, high-density lipoprotein; HOMA-IR, homeostatic model assessment of insulin resistance; LDL, low-density lipoprotein; SD, standard deviation.