Spock underestimates his mother's abilities to his detriment.
Female Intuition
Spock concluded that the only logical way to get the answers he sought was to study the experiences of other multicultural couples. Vulcan/Human pairings were not unheard of but they were still extremely rare, so his best resource was his parents. But not his Sarek, not unless he absolutely had to. First, he had to arrange to speak to his mother at a time when he knew for certain she would be alone. His father's evening meditation period would suffice since it was well past normal working hours. He was able to secure a channel to Vulcan once the Enterprise entered the outer limits of Vulcan territory.
"Hello, Mother. You look agreeable as always," Spock spoke into the viewer located in his office. Uhura was asleep in their quarters and he did not wish to disturb her nor did he want her to worry about their situation any more than necessary.
"Only agreeable? I see marriage has not changed you one bit," Amanda said, smiling brightly.
"On the contrary, Mother, I have changed a great deal since my bonding to Nyota. In fact, that is the reason for this call."
"Oh? What's wrong now?" she said, becoming serious, matching Spock's somber tone.
"I have some questions about Vulcan/Human relationships and about human females in particular."
"Oh," she said, relaxing again, "that's all? That doesn't sound too serious. Is there a new problem with your relationship with Nyota? I thought you two had finally worked everything out since the trial?"
It displeased Spock to hear Amanda's reply. He had confided to his mother many of the details in the ongoing relationship drama between Nyota and himself. Now he regretted sharing so much of his personal struggles with her. He realized he had burdened her unnecessarily. He should have known as a human, his mother would take his problems on as her own and have an emotional reaction to them.
"Mother, I must apologize for any grief that my recent troubles with Nyota have caused you. I regret that the unconventional method of our bonding has created problems for you, not just within our clan, but within Starfleet and with the Federation. You and Father and T'Pau have been more than generous with your assistance, and Nyota and I are very grateful."
Amanda dismissed his apology. "Your thanks are illogical. You're my child and I love you. And I'll fight for your happiness with my dying breath."
Spock only nodded in acknowledgment. After all these years, he still didn't know how to respond to his mother's love. "Mother, I must once again ask for your guidance. And the question is of a nature that only you can provide the answer."
Amanda understood her son quite well and knew she had flustered him, so she put on her serious2 Vulcan face. "Okay. What is it, my son?"
"As you say, Nyota and I have been getting along quite well in solidifying our bond. In fact, it has come to my attention that perhaps we are getting along a bit too well?" Spock offered hesitantly.
"How's that? How can you get along too well?" Amanda asked, in total confusion.
"That is the question I must pose to you. As you know, Nyota and I share a unique bond since she has part of my Katra..."
"Yes, yes, I know, but is that a cause for concern? T'Pau didn't seem to think so. Like any ordinary couple, you two just needed to strengthen the bond you have so that you can maintain your equilibrium until the Time comes. Surely the incident with T'Pring emphasizes the dangers of a weak marital bond?"
"I have no doubt that my bond with Nyota is strong and stable. However, even after the Pon Farr abated, Nyota and I have experienced certain lingering symptoms."
"Pon Farr symptoms?" This caught Amanda's attention.
"Yes, having recently made our bond official-"
"Official?" Amanda interrupted, laughing and shaking her head. "There is nothing more official than a Vulcan marriage bond, except a shared Katra, of course."
"Yes, Mother. However, Nyota and I had not disclosed our marital status to many people except our closest friends and family. That is until the trial. Now that everyone knows we are married, it is official. I have even given Nyota a wedding ring. There is no doubt about the status of our relationship."
"Oh my. Imagine my son being so grown up and 'officially married'?" Amanda smiled with a dreamy look on her face.
"As I was saying, after the trial I gave Nyota a ring and I moved my belongings into her quarters. Hence, we are officially out to the crew. However, as we become more accustomed to the bond we share, we have experienced several unforeseen consequences."
"The Pon Farr symptoms?"
"Yes."
"What are they?"
"Well, ahem," Spock felt his face heat up, but he continued anyway, ignoring his mother's knowing smirk. "Nyota and I have both experienced intense, um... sexual attraction..."
"That's all?" she smiled, barely containing a laugh.
"It is more than mere sexual attraction. It is difficult to describe..." Spock experienced some frustration before he could control it.
"Oh, really?" Amanda said, becoming more suspicious of Spock's reluctance to talk. "Try."
"Nyota... has an intense attachment to me. That is to say, Nyota has told me when we are separated for any length of time she feels anxiety. And when we are together, she feels intense... um... arousal, and she wants to... um... please me. And she feels compelled to obey me. I believe these intense emotions are somehow being shared by us, possibly because of my Katra. Nyota described it as addiction."
"Oh my, that is interesting," Amanda said, scrunching her nose in thought.
"Indeed?" he asked, eagerly awaiting a solution to the problem.
"Yes. It sounds romantic," she teased. She wasn't taking this seriously at all.
"Mother! Please?" Why was his mother always like this!
"Alright, alright. Just what is it that you want from me? What is it that only I can answer?"
"Did you ever experience any such phenomenon after your bonding with my father?"
"Are you asking, does bonding with a Vulcan make human women extremely amorous and eager to please? No. Not that I can recall, and I recall my bonding very well." She smiled in fond remembrance.
"Yes, Mother, that is what I am asking you."
Amanda beamed an enormous grin. "So you and Nyota are getting along very well indeed? That is good to hear. And hopefully, it won't be long before-" Amanda stopped short, catching her breath. "No!" she said in a deep throaty voice that indicated disbelief.
"What is it, Mother?" Spock asked anxiously. His mother knew something, he was certain of it.
"I remember!"
"What do you remember, Mother?"
"When I was pregnant with you, I was absolutely obsessed with Sarek. I couldn't stand to be away from your father, even for a few hours. And when we were together, all I wanted to do was... Well, you know. Your father was such a dear, he could hardly do his work, with me being sick one moment and so sexed up the next..." Amanda smiled, remembering one of the happiest times of her life. Then her smile faltered for a moment while she thought. "Spock! Oh my god! Baby! Are you having a baby?! Is Nyota pregnant?"
"Mother-"
"That's it, isn't it? Nyota is pregnant! It all sounds exactly like my pregnancy. I was so horny ALL the time, and it affected your father too. He was very accommodating to me. The healers said it was some Vulcan pheromones we humans develop..." Amanda was babbling excitedly now, bouncing up and down in her seat.
"Yes! Finally!," she threw her hands up in the air and clapped. "Oh, my darling! I'm so happy for you!" she started crying.
All the commotion must have disturbed Sarek's meditation. He appeared behind Amanda and took her in his arms.
"What is it, my wife?" Sarek asked with a concerned voice.
"Spock!" Amanda pointing at the viewer and buried her face into Sarek's chest, dabbing her eyes on the pleats of his robe.
"What has happened to Spock?" Sarek bent down to look at the viewer.
He looked visibly relieved to see his son on the screen, looking whole and healthy. "Spock, what has happened?"
"Father," Spock said with resignation. The cat, to use a colloquial term, was out of the bag. "Nothing has happened to me. Mother has merely jumped to conclusions. I apologize for the inconvenience I have caused you."
"You have not inconvenienced me, but you have upset your mother." Sarek turned his attention to Amanda to comfort her.
"Mother, I regret that I have evoked such emotion," Spock said to Amanda.
"Amanda, what is the cause of all of this?" Sarek asked.
"Spock is having a baby!"
"Is he indeed?" Sarek looked into the viewer again, a questioning expression on his face.
"Sarek," she said, swatting at him playfully, "Nyota is pregnant! They are going to have a baby!"
"Is this true, Spock?" Sarek asked with a look of astonishment on his normally placid face.
He couldn't lie to his parents, therefore he was forced to break his promise to Nyota. "Mother, Father, please. This is not something we are sharing with anyone yet. Not even Nyota's family knows. Nyota does not want anyone to know until we disclose it officially."
"Then why did you tell your mother?" Sarek asked.
"I did not tell her, she deduced it on her own."
"Amanda deduced it?" Sarek sounded surprised while he looked down at his wife.
"Yes," Amanda answered. "Spock described the strange symptoms he and Nyota were having and it reminded me of us back when I was carrying..."
"I see," Sarek nodded.
"And he didn't deny it either," she said defensively.
"It would hardly be logical to deny the truth, which you would be told eventually," Spock said.
"Congratulations, sweetheart! Oh, I need to call Nyota," she said, bouncing with excitement again.
"Mother, please do not. I told you she is not ready to acknowledge her pregnancy."
"Why? Is everything alright? You said she had symptoms? I remember I was terribly sick while carrying you..." Amanda said, sobering a bit.
"Nyota is fine. She had one fainting spell and a panic attack, but so far all is well. Doctor McCoy would like her to take it easy for a while on light duty when she is up to it."
"How far along is she?" Amanda's mind was all in on this pregnancy now, and any other concern was lost on her.
"The good doctor speculates that conception occurred during my Pon Farr but it could also have occurred during Nyota's own fever."
Sarek nodded. "Ah, just as I suspected," Sarek said while looking down at Amanda.
"You suspected it?" she asked, looking up at Sarek.
"I speculated there was a high probability of increased fertility. As I recall, I advised Dr. McCoy that his contraceptive efforts were in vain."
"I didn't know that," Amanda said.
"It is a matter of common knowledge that birth control has no effect during Pon Farr."
"If that were true... well, I guess I never needed that information. I never needed birth control," Amanda said sadly.
"Amanda, the boy is listening."
Spock wanted to say "the boy is a full-grown man," but he refrained. His parents still had a way of bringing out the insecure boy in him after all these years.
"Mother, is there anything else you can disclose about our newly acquired status?"
"Well," Amanda said, wiping her eyes. She was still weeping tears of joy. "Your father could probably explain it all a lot better than I could. I was a hormonal wreck at the time. I could dig out my old diaries if you think that would be helpful."
Spock imagined reading page after page of his mother's emotional ramblings and intimate secrets and declined the offer. "I do not think that will be necessary, Mother."
"I'll send them to Nyota. She may find them interesting," Amanda said, ignoring Spock and making plans of her own.
Spock sensed his mother was a lost cause. "Father?" Spock asked, hoping for more practical advice.
"Spock, there were indeed complications to your gestation. Your mother and I both shared some symptoms brought on by increased hormone production in your mother. Increased sexual arousal. Also increased attachment, hypervigilance, and heightened protective instincts. The usual mate-guarding behaviors," Sarek said.
The usual? Spock wondered. Since when was any of that usual for a Vulcan. But then he remembered he had not lived on Vulcan for many years. He had left home when he was but a young man. He had no experience with young married Vulcan couples or pregnant Vulcan women. He had a lot to learn about his homeworld and her people if he were to guide Nyota successfully through this process.
"Are there any reference materials I may access to better acquaint myself with what we can look forward to?"
"Spock, you know our ways and how we pass on such information," Sarek reminded him.
"Yes, I know," Spock answered. Anything having to do with reproduction, and Pon Farr was passed on orally, generation to generation, father to son, mother to daughter. Spock controlled his desire to sigh in resignation. He wished he could talk to Sybok about all this. Sybok would not hesitate to tell Spock everything he ever wanted to know about any subject and quite a few things he didn't want to know. But Sybok was long gone, and all he had was Sarek. He would have to have a long talk with his father. One that was well overdue.
Spock was not looking forward to that conversation. And now he had to tell Nyota that he had inadvertently told his parents about the pregnancy. To borrow one of his wife's emotional expletives, "Oh shit!"
Note: Sometimes I catch myself writing that Spock felt this or that and I have to remember he's not supposed to feel those things. I know he has the feelings, but he's suppressing them. Sigh. But that's what makes him so beloved by the fandom, right?