Table 1.
Unadjusted and Propensity-Score–Adjusted Baseline Characteristics of Lithium-Exposed and Unexposed Pregnant Women.*
| Characteristic | Unadjusted | Propensity-Score–Adjusted† | ||
|---|---|---|---|---|
| No Exposure |
Exposure to Lithium |
No Exposure |
Exposure to Lithium |
|
| No. of pregnancies | 1,322,955 | 663 | 928,767 | 663 |
|
| ||||
| Age — yr | 24.0±5.8 | 25.6±6.1‡ | 25.6±6.2 | 25.6±6.1 |
|
| ||||
| Race or ethnic group — no. (%)§ | ||||
|
| ||||
| White | 526,603 (39.8) | 490 (73.9)‡ | 708,409 (76.3) | 490 (73.9) |
|
| ||||
| Black | 445,675 (33.7) | 89 (13.4)‡ | 113,987 (12.3) | 89 (13.4) |
|
| ||||
| Hispanic | 195,174 (14.8) | 36 (5.4)‡ | 41,876 (4.5) | 36 (5.4) |
|
| ||||
| Other | 155,503 (11.8) | 48 (7.2)‡ | 64,495 (6.9) | 48 (7.2) |
|
| ||||
| Psychiatric and neurologic conditions — no. (%) | ||||
|
| ||||
| Bipolar disorder | 9,485 (0.7) | 436 (65.8)‡ | 608,904 (65.6) | 436 (65.8) |
|
| ||||
| Depression | 63,110 (4.8) | 167 (25.2)‡ | 257,475 (27.7) | 167 (25.2) |
|
| ||||
| Anxiety | 41,759 (3.2) | 117 (17.6)‡ | 179,054 (19.3) | 117 (17.6) |
|
| ||||
| Pain conditions¶ | 183,219 (13.8) | 184 (27.8)‡ | 272,867 (29.4) | 184 (27.8) |
|
| ||||
| Chronic maternal illness — no. (%) | ||||
|
| ||||
| Hypertension | 24,529 (1.9) | 22 (3.3) | 30,197 (3.3) | 22 (3.3) |
|
| ||||
| Diabetes | 23,287 (1.8) | 18 (2.7) | 26,222 (2.8) | 18 (2.7) |
|
| ||||
| Psychotropic and other medications — no. (%) | ||||
|
| ||||
| Antidepressants | 106,412 (8.0) | 431 (65.0)‡ | 641,793 (69.1) | 431 (65.0) |
|
| ||||
| Antipsychotic agents | 12,366 (0.9) | 308 (46.5)‡ | 394,767 (42.5) | 308 (46.5) |
|
| ||||
| Benzodiazepines | 34,932 (2.6) | 207 (31.2)‡ | 283,907 (30.6) | 207 (31.2) |
|
| ||||
| Other anxiolytic agents | 4,288 (0.3) | 31 (4.7)‡ | 41,285 (4.4) | 31 (4.7) |
|
| ||||
| Other hypnotic agents | 43,150 (3.3) | 114 (17.2)‡ | 154,213 (16.6) | 114 (17.2) |
|
| ||||
| Opioids | 249,821 (18.9) | 253 (38.2)‡ | 370,867 (39.9) | 253 (38.2) |
|
| ||||
| Markers of the burden of disease | ||||
|
| ||||
| Obstetric Comorbidity Index║ | 0.9±1.4 | 1.6±1.8‡ | 1.6±1.8 | 1.6±1.8 |
|
| ||||
| No. of distinct prescriptions | 1.6±2.3 | 4.5±3.7‡ | 4.6±3.7 | 4.5±3.7 |
|
| ||||
| No. of outpatient physician visits | 2.8±4.0 | 8.5±9.8‡ | 8.0±8.5 | 8.5±9.8 |
|
| ||||
| Patients hospitalized — no. (%) | 48,294 (3.7) | 60 (9.0)‡ | 81,082 (8.7) | 60 (9.0) |
Plus–minus values are means ±SD. Maternal coexisting conditions and medication use were measured during the 3 months before pregnancy through the end of the first trimester. Measures of health care use (e.g., number of physician visits) were captured only during the 3 months before pregnancy to avoid their being influenced by early awareness of possible pregnancy complications. Percentages may not sum to 100 because of rounding.
Exposure propensity scores were estimated as the predicted probability of receiving lithium versus no treatment, conditional on the covariates reported in Table S2 in the Supplementary Appendix. For each estimated propensity score, the population in the nonoverlapping areas of the propensity-score distributions was trimmed, and 50 strata were created on the basis of the distribution of the treated women. Weights for the reference group were calculated according to the distribution of the exposed women among propensity-score strata and were used to estimate adjusted baseline characteristics.
There was a meaningful between-group imbalance, as assessed by an absolute standardized difference of more than 0.1.36
Race or ethnic group was identified from Medicaid enrollment files. Other race includes Asian, Native American, other, and unknown.
Pain conditions include neuropathic and nonneuropathic conditions.
The Obstetric Comorbidity Index predicts severe maternal illness. The range is 0 to 45, with higher values associated with a higher burden of maternal illness.35