Page 89 - Fertility in Women with Rheumatoid Arthritis Vruchtbaarheid van vrouwen met reumatoïde artritis

prednisone or sulfasalazine, preconceptional use of non-steroidal anti-inflammatory drugs (NSAIDs), and use of methotrexate in the past.
Subfertility was de ned as not achieving pregnancy after 12 months of trying to conceive.
Measurements
Disease activity was measured using a tender and swollen joint count for 28 joints, combined with serum C reactive protein (CRP) levels (DAS28-CRP).27 Details on the measurement of RF and ACPA can be found in the original report on the PARA study.26 Serum samples were stored at -80°C. Serum AMH levels (ug/L or ng/ml) were measured using pico AMH assay developed by Ansh Labs (Houston,Texas, USA).28 The Limit of Detection (LoD) was 0.0012 ug/L.
Controls
Serum AMH values were compared to those of an existing healthy control group
consisting of 554 adult women aged 18-47 years, who had regular menstrual cycles,
and of whom the majority was proven fertile.12 Since serum AMH levels in the control
group were reported as values measured with the GenII Beckman Coulter assay, a
conversion factor was used to compare the AMH levels in the patient group to those 6 in the controls:29
AMH (pico AMH assay in ng/mL) = (1.45 * AMHGen II) + 0.32
Statistics
Serum AMH levels were skewed to the right and were log-transformed for analysis. To make log-transformation possible, serum AMH levels below the LoD (0.0012 ug/L), were imputed by dividing the LoD by the square root of 2.30 Numbers of missing values were reported. Missing values were imputed using multiple imputation with chained equations. All variables of interest (see Data collection) that had missing values were included in the imputation, as well as all other variables intended to be put into the Cox proportional hazard analysis. Because of the survival nature of the data, also the event variable _d (occurrence of pregnancy) and the Nelson Aalen estimator (estimation of baseline hazard H0(t)) were included in the imputation procedure.31 Being outcome variables, missing values of _d and the Nelson Aalen estimator were not imputed.
An analysis of covariance (ANCOVA) was performed to compare log-transformed AMH levels, corrected for age, between RA patients and controls. Associations of various
AMH in RA – time to pregnancy
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