Use of levothyroxine among pregnant women with subclinical hypothyroidism in the United Kingdom: A population‐based assessment

Abstract

Our study aimed to describe levothyroxine prescription patterns and trends over time among pregnant women with subclinical hypothyroidism (SCH) in the United Kingdom. We used data from the Clinical Practice Research Datalink linked to its Pregnancy Register and the Hospital Episode Statistics database from 1998 to 2017. The study population included women with a diagnosis of SCH or an abnormal thyroid‐simulated hormone (TSH) level one year prior to or during pregnancy. We compared characteristics between women who received a prescription for levothyroxine during pregnancy and those who did not. We further described the timing, dose, duration, and temporal trends of levothyroxine prescriptions. Our cohort included 6,757 pregnancies from 6,287 women with SCH, of whom 10% received levothyroxine during pregnancy. Among women who received levothyroxine, most received their first prescription during the first trimester (median gestational age: 7 weeks; interquartile range [IQR]: 0, 16) with a median daily dosage of 50 mcg (IQR: 50, 73). Levothyroxine prescription varied over time, decreasing from 23% of pregnant women in 1998 to 7.5% in 2003, remaining stable until 2014, and increasing to 12.5% in 2016. Smoking, diabetes, polycystic ovary syndrome, infertility, timing of SCH diagnosis, age, TSH level at diagnosis, and general practice regions were associated with prescription. Few women with SCH received levothyroxine during pregnancy, and treatment varied by patient characteristics and geographical regions. These results highlight the need to increase awareness among healthcare providers and will guide future studies that explore barriers to initiating levothyroxine treatment for women with SCH during pregnancy.

Effect of levothyroxine on gestational hypertension and pre-eclampsia in subclinical hypothyroidism, hypothyroidism, and thyroid autoimmunity: a systematic review and meta-analysis

“…Two hypotheses compared SCH with placebo in RCT (16) and cohort (25) studies. Eight hypotheses (14,17,(20)(21)(22)(23)27) compared treated SCH with untreated SCH. The trimester of study entry in ten was rst, ve was second, one was third, three were rst or second, and in one was rst, second, or third trimesters.…”

“…The trimester of study entry in ten was rst, ve was second, one was third, three were rst or second, and in one was rst, second, or third trimesters. For GH outcome, the time to start treatment was during gestation except for one that was unknown (25) and another (27) that was before or during pregnancy; and for PE outcome, in all was during pregnancy.…”

“…The sensitivity analysis results indicated that after excluding each study, the total effect size did not change. For GH, all studies were cohort except one, which was RCT (27). For PE, two studies were cohort, and three studies were RCT.…”

Systematic review and meta-analysis of the efficacy and pregnancy outcomes of levothyroxine sodium tablet administration in pregnant women complicated with hypothyroidism

“…A study of SCH patients treated with levothyroxine sodium tablets until delivery found that the incidence of adverse maternal and infant outcomes was significantly lower in patients treated with levothyroxine sodium tablets (11). In addition, Yu et al [2021] used levothyroxine sodium tablets and thyroxine tablets to treat patients with hypothyroidism in late pregnancy; the results found that the incidence of adverse pregnancy in pregnant women treated with levothyroxine sodium tablets was significantly lower than that in pregnant women treated with thyroxine tablets (12). However, the current evidence for levothyroxine sodium tablets for the treatment of SCH is still insufficient (13).…”

Under and overtreatment with thyroid hormone replacement during pregnancy

“…Studies published prior to the 2017 American Thyroid Association (ATA) guideline [2] showed that 43% of studied pregnant women in the United States [3], 55% in the UK [4], and 50.9% in Sweden [5], had first-trimester TSH values above the target range. Over the last decade there has been a trend toward increasing use of LT4 during gestation in multiple regions, including the United States [6], Canada [7 ▪ ], Sweden [8 ▪ ], and Norway [9 ▪ ]. However, despite these increases, most eligible women may remain untreated [6].…”