La donna incinta vede il medico.

They are the Italian definite articles, equivalent to the.

• la goes with a feminine singular noun: la donna
• il goes with a masculine singular noun: il medico

So the articles have to agree with the gender and number of the noun they go with.

Because medico begins with a normal consonant sound, m.

Italian uses:

• il before most masculine singular nouns beginning with a consonant
• lo before special consonant clusters such as s + consonant, z, gn, ps, x, and a few others

So:

• il medico
• but lo studente, lo zio

In Italian, adjectives often come after the noun they describe.

So:

• la donna incinta = the pregnant woman

That is the most natural order here. Some adjectives can come before the noun, but that often sounds more literary, stylistic, or changes the nuance. With incinta, putting it after the noun is the normal choice.

Because incinta is being used inside the noun phrase, not as the main predicate of the sentence.

Compare:

• la donna incinta = the pregnant woman
• la donna è incinta = the woman is pregnant

So in your sentence, incinta is just describing donna directly. No form of essere is needed.

Because the adjective has to agree with donna, which is feminine singular.

Italian adjectives usually agree in gender and number with the noun they modify. Here:

• donna = feminine singular
• so the adjective is incinta

For example, with a plural feminine noun you would get:

• le donne incinte

Vede is the third-person singular present tense of vedere.

So it means:

• he sees
• she sees
• it sees

In this sentence, the subject is la donna incinta, so vede means she sees.

Because Italian usually does not need subject pronouns when the subject is already clear.

Here the subject is explicitly stated:

• La donna incinta vede il medico.

So adding lei would usually be unnecessary unless you wanted extra emphasis or contrast.

This is very common in Italian: the verb ending and the sentence context usually make the subject clear.

In a normal sentence like this, Italian usually follows subject + verb + object order.

So:

• La donna incinta = subject
• vede = verb
• il medico = object

That means the pregnant woman is the one who sees, and the doctor is the one being seen.

If you reversed the two noun phrases, the meaning would normally reverse too:

• Il medico vede la donna incinta. = The doctor sees the pregnant woman.

In this sentence, il medico is grammatically masculine singular, so it most naturally refers to a male doctor.

If you were clearly referring to a woman, you might see:

• la dottoressa
• or la medica in some usage

The exact choice can vary by region, register, and personal preference, but in your sentence il medico is masculine.

Yes, but the meaning would change slightly.

• La donna incinta vede il medico. = a specific pregnant woman sees a specific doctor, or the sentence is talking about them as known people
• Una donna incinta vede un medico. = a pregnant woman sees a doctor, more indefinite and less specific

So the grammar is the same, but the articles change how specific the people are.

Not in normal standard Italian prose or speech.

Italian usually requires articles with nouns in sentences like this:

• la donna
• il medico

Leaving them out would sound unnatural, except in very special contexts such as headlines, notes, or very telegraphic language. In an ordinary full sentence, you should keep the articles.