Why do LH levels change during the luteal phase, and what does a second LH surge after ovulation mean?Updated a month ago
LH is secreted in discrete pulses throughout the cycle, and the pulse pattern shifts by phase. In the luteal phase, progesterone from the corpus luteum slows the hypothalamic GnRH pulse generator, reducing pulse frequency while pulse amplitude rises above follicular-phase levels (Rossmanith, 1991). Because Mira quantifies actual LH concentration rather than returning a binary positive, it will capture these normal high-amplitude luteal pulses.
A second peak occurring within a day or two of the primary surge frequently reflects the configuration of the surge itself rather than a separate event. In a prospective analysis of 283 cycles in normally fertile women, only 48% of surges were single-peaked; 33% were double-peaked, 8% multi-peaked, and 11% plateaued (Direito et al., 2012). Interpreting the whole curve, rather than a single elevated reading, is therefore essential.
A clinically important cause of an apparent luteal-phase LH rise is hCG cross-reactivity. LH and hCG are heterodimeric glycoprotein hormones that share an identical alpha subunit, and their beta subunits are highly homologous — hCG-beta is essentially LH-beta with a C-terminal extension — so both bind the common LH/hCG receptor and can be recognized by the same antibodies (Nakabayashi et al., 2002; Tayapiwatana & Poonpipat, 1998).
LH immunoassays can therefore cross-react with hCG to a degree that depends on antibody epitope specificity. Practically, a rise late in the luteal phase — coinciding with the implantation window from roughly 8 days post-ovulation onward — may represent early-pregnancy hCG being detected by the LH assay rather than an LH event at all.
A true second ovulation is not a plausible explanation: once the corpus luteum forms, luteal-phase progesterone suppresses recruitment of a new dominant follicle within the same cycle. Where a luteal LH pattern does carry clinical weight is in prolonged or fragmented surges.
Direito et al. found surges with multiple peaks were associated with smaller pre-rupture follicle diameters and lower peak LH, and surges persisting more than three days beyond ovulation were associated with lower pre-ovulatory estrogen, a smaller corpus luteum, and lower luteal progesterone — findings consistent with suboptimal corpus luteum function. An isolated second peak, by contrast, is not diagnostic in itself. Toward the end of the luteal phase, LH also rises again physiologically as the corpus luteum regresses and progesterone withdraws.
Sources: Direito A, Bailly S, Mariani A, Ecochard R. Fertil Steril. 2012;99(1):279-285 — DOI. Rossmanith WG. Geburtshilfe Frauenheilkd. 1991;51(8):585-594 — DOI. Nakabayashi K, et al. J Clin Invest. 2002;109(11):1445-1452 — DOI. Tayapiwatana C, Poonpipat P. Asian Pac J Allergy Immunol. 1998;16(2-3):127-135 (PubMed PMID 9876951). Articles retrieved from PubMed.