Wikitionary shows a PIE word *méh₂tēr but I never seen this word spelled with a laryngeal. There was a long vowel there but how is it correct to analyze it to be *-eh₂- rather than just *ā?
Depending upon the specific view that one accepts concerning the development of the accent systems of Baltic and Slavic, the Baltic cognate would compel a reconstruction with *h2.
Lithuanian (nom.) móteris [the acute diacritic here indicates the surface word accent] ‘woman’ belongs to the third accent class, which indicates that the stem moteri- contained a so-called "acute" intonation (the use of the terms "acute" and "circumflex" in Baltic and Slavic accentology is fraught and convoluted -- beware). If one follows the position of Kortlandt (though also more or less sustained in Petit's recent Untersuchungen zu den baltischen Sprachen) that only IE laryngeals or voiced stops in syllable codas could eventually produce "acute" intonation, then the reconstruction *meh2-ter- would be necessary.
Furthermore, insofar as one does analyze the word into a root and suffix -ter, no IE root whatsoever that participates in derivation lacks a consonant following the root's full-grade (confer the roots in the Lexicon der Indogermanischen Verben). IE grammatical elements that lack final consonants consist exclusively of particles (e.g., *su 'good, well'), prepositions (e.g., *pro ‘before’), and pronouns. Thus, IE constraints on licit root structures would exclude *mā- as a root. So even setting the Baltic considerations aside, *meh2-ter remains a preferable reconstruction.