Which meaning of "to conceive" came first?

I had a look for you in the OED and here is the most interesting part (highlight is mine):

[a. OF. concev-eir, -oir, (stressed stem conˈceiv-):—L. concipĕre, f. con- altogether + capĕre to take. The F. form of the word is assimilated to verbs in -ēre, while other Romanic langs. have -ĕre, -īre: cf. Pr. concebre, Sp. concebir, It. concépere and -cepére. Nearly all the senses found in Fr. and Eng. were already developed in L., where the primary notion was app. ‘to take effectively, take to oneself, take in and hold’. The development is thus partly parallel to that of catch (esp. in branches VII, VIII), which word may be substituted for conceive in some uses.]

Having understood that the various senses already existed in the Latin word concipĕre, I turned to the extensive Perseus corpus of Latin works, which I warmly recommend.

I did not read all of the 5 pages of results. I just focused on classical Latin.

• Cicero, Livy use it in a great variety of ways (conceive feelings or ideas "have a take on" events).
• Pliny and Lucretius use extensively the term in its biological sense.
• Later scholar works also use it in a medical sense of "showing symptoms of" (fever).

I also looked up concipio in the Oxford Latin Dictionary (1968) and there are no less than 13 different meanings for this verb. Only 2 of them in the sense of to "engender".

So there's no clear cut answer even in classical Latin, I'm afraid.

The only indication comes from the OED clause "where the primary notion was app. ‘to take effectively, take to oneself, take in and hold".

Etymonline reports that conceive with the meaning of "become pregnant" is from late 13th century, while with the meaning of "take into the mind" is from middle 14th century.
The figurative sense was also used in Latin, and Old French.